The Collaborative International Dictionary of English v.0.48:

Flat \Flat\ (fl[a^]t), a. [Compar. Flatter (fl[a^]t"r[~e]r);
   superl. Flattest (fl[a^]t"t[e^]st).] [Akin to Icel. flatr,
   Sw. flat, Dan. flad, OHG. flaz, and AS. flet floor, G.
   fl["o]tz stratum, layer.]
   1. Having an even and horizontal surface, or nearly so,
      without prominences or depressions; level without
      inclination; plane.
      [1913 Webster]

            Though sun and moon
            Were in the flat sea sunk.            --Milton.
      [1913 Webster]

   2. Lying at full length, or spread out, upon the ground;
      level with the ground or earth; prostrate; as, to lie flat
      on the ground; hence, fallen; laid low; ruined; destroyed.
      [1913 Webster]

            What ruins kingdoms, and lays cities flat! --Milton.
      [1913 Webster]

            I feel . . . my hopes all flat.       --Milton.
      [1913 Webster]

   3. (Fine Arts) Wanting relief; destitute of variety; without
      points of prominence and striking interest.
      [1913 Webster]

            A large part of the work is, to me, very flat.
                                                  --Coleridge.
      [1913 Webster]

   4. Tasteless; stale; vapid; insipid; dead; as, fruit or drink
      flat to the taste.
      [1913 Webster]

   5. Unanimated; dull; uninteresting; without point or spirit;
      monotonous; as, a flat speech or composition.
      [1913 Webster]

            How weary, stale, flat, and unprofitable
            Seem to me all the uses of this world. --Shak.
      [1913 Webster]

   6. Lacking liveliness of commercial exchange and dealings;
      depressed; dull; as, the market is flat.
      [1913 Webster]

   7. Clear; unmistakable; peremptory; absolute; positive;
      downright.

   Syn: flat-out.
        [1913 Webster]

              Flat burglary as ever was committed. --Shak.
        [1913 Webster]

              A great tobacco taker too, -- that's flat.
                                                  --Marston.
        [1913 Webster]

   8. (Mus.)
      (a) Below the true pitch; hence, as applied to intervals,
          minor, or lower by a half step; as, a flat seventh; A
          flat.
      (b) Not sharp or shrill; not acute; as, a flat sound.
          [1913 Webster]

   9. (Phonetics) Sonant; vocal; -- applied to any one of the
      sonant or vocal consonants, as distinguished from a
      nonsonant (or sharp) consonant.
      [1913 Webster]

   10. (Golf) Having a head at a very obtuse angle to the shaft;
       -- said of a club.
       [Webster 1913 Suppl.]

   11. (Gram.) Not having an inflectional ending or sign, as a
       noun used as an adjective, or an adjective as an adverb,
       without the addition of a formative suffix, or an
       infinitive without the sign to. Many flat adverbs, as in
       run fast, buy cheap, are from AS. adverbs in -["e], the
       loss of this ending having made them like the adjectives.
       Some having forms in ly, such as exceeding, wonderful,
       true, are now archaic.
       [Webster 1913 Suppl.]

   12. (Hort.) Flattening at the ends; -- said of certain
       fruits.
       [Webster 1913 Suppl.]

   Flat arch. (Arch.) See under Arch, n., 2. (b).

   Flat cap, cap paper, not folded. See under Paper.

   Flat chasing, in fine art metal working, a mode of
      ornamenting silverware, etc., producing figures by dots
      and lines made with a punching tool. --Knight.

   Flat chisel, a sculptor's chisel for smoothing.

   Flat file, a file wider than its thickness, and of
      rectangular section. See File.

   Flat nail, a small, sharp-pointed, wrought nail, with a
      flat, thin head, larger than a tack. --Knight.

   Flat paper, paper which has not been folded.

   Flat rail, a railroad rail consisting of a simple flat bar
      spiked to a longitudinal sleeper.

   Flat rods (Mining), horizontal or inclined connecting rods,
      for transmitting motion to pump rods at a distance.
      --Raymond.

   Flat rope, a rope made by plaiting instead of twisting;
      gasket; sennit.

   Note: Some flat hoisting ropes, as for mining shafts, are
         made by sewing together a number of ropes, making a
         wide, flat band. --Knight.

   Flat space. (Geom.) See Euclidian space.

   Flat stitch, the process of wood engraving. [Obs.] -- Flat
   tint (Painting), a coat of water color of one uniform shade.


   To fall flat (Fig.), to produce no effect; to fail in the
      intended effect; as, his speech fell flat.
      [1913 Webster]

            Of all who fell by saber or by shot,
            Not one fell half so flat as Walter Scott. --Lord
                                                  Erskine.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flat \Flat\, v. t. [imp. & p. p. Flatted; p. pr. & vb. n.
   Flatting.]
   1. To make flat; to flatten; to level.
      [1913 Webster]

   2. To render dull, insipid, or spiritless; to depress.
      [1913 Webster]

            Passions are allayed, appetites are flatted.
                                                  --Barrow.
      [1913 Webster]

   3. To depress in tone, as a musical note; especially, to
      lower in pitch by half a tone.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flat \Flat\, n.
   1. A level surface, without elevation, relief, or
      prominences; an extended plain; specifically, in the
      United States, a level tract along the along the banks of
      a river; as, the Mohawk Flats.
      [1913 Webster]

            Envy is as the sunbeams that beat hotter upon a
            bank, or steep rising ground, than upon a flat.
                                                  --Bacon.
      [1913 Webster]

   2. A level tract lying at little depth below the surface of
      water, or alternately covered and left bare by the tide; a
      shoal; a shallow; a strand.
      [1913 Webster]

            Half my power, this night
            Passing these flats, are taken by the tide. --Shak.
      [1913 Webster]

   3. Something broad and flat in form; as:
      (a) A flat-bottomed boat, without keel, and of small
          draught.
      (b) A straw hat, broad-brimmed and low-crowned.
      (c) (Railroad Mach.) A car without a roof, the body of
          which is a platform without sides; a platform car.
      (d) A platform on wheel, upon which emblematic designs,
          etc., are carried in processions.
          [1913 Webster]

   4. The flat part, or side, of anything; as, the broad side of
      a blade, as distinguished from its edge.
      [1913 Webster]

   5. (Arch.) A floor, loft, or story in a building; especially,
      a floor of a house, which forms a complete residence in
      itself; an apartment taking up a whole floor. In this
      latter sense, the usage is more common in British English.
      [1913 Webster +PJC]

   6. (Mining) A horizontal vein or ore deposit auxiliary to a
      main vein; also, any horizontal portion of a vein not
      elsewhere horizontal. --Raymond.
      [1913 Webster]

   7. A dull fellow; a simpleton; a numskull. [Colloq.]
      [1913 Webster]

            Or if you can not make a speech,
            Because you are a flat.               --Holmes.
      [1913 Webster]

   8. (Mus.) A character [[flat]] before a note, indicating a
      tone which is a half step or semitone lower.
      [1913 Webster]

   9. (Geom.) A homaloid space or extension.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flat \Flat\, adv.
   1. In a flat manner; directly; flatly.
      [1913 Webster]

            Sin is flat opposite to the Almighty. --Herbert.
      [1913 Webster]

   2. (Stock Exchange) Without allowance for accrued interest.
      [Broker's Cant]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flat \Flat\, v. i.
   1. To become flat, or flattened; to sink or fall to an even
      surface. --Sir W. Temple.
      [1913 Webster]

   2. (Mus.) To fall form the pitch.
      [1913 Webster]

   To flat out, to fail from a promising beginning; to make a
      bad ending; to disappoint expectations. [Colloq.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

flat
    adv 1: with flat sails; "sail flat against the wind"
    2: in a forthright manner; candidly or frankly; "he didn't
       answer directly"; "told me straight out"; "came out flat for
       less work and more pay" [syn: directly, flat, straight]
       [ant: indirectly]
    adj 1: having a surface without slope, tilt in which no part is
           higher or lower than another; "a flat desk"; "acres of
           level farmland"; "a plane surface"; "skirts sewn with
           fine flat seams" [syn: flat, level, plane]
    2: having a relatively broad surface in relation to depth or
       thickness; "flat computer monitors"
    3: not modified or restricted by reservations; "a categorical
       denial"; "a flat refusal" [syn: categoric, categorical,
       flat, unconditional]
    4: stretched out and lying at full length along the ground;
       "found himself lying flat on the floor" [syn: flat,
       prostrate]
    5: lacking contrast or shading between tones [ant: contrasty]
    6: (of a musical note) lowered in pitch by one chromatic
       semitone; "B flat" [ant: natural, sharp]
    7: flattened laterally along the whole length (e.g., certain
       leafstalks or flatfishes) [syn: compressed, flat]
    8: lacking taste or flavor or tang; "a bland diet"; "insipid
       hospital food"; "flavorless supermarket tomatoes"; "vapid
       beer"; "vapid tea" [syn: bland, flat, flavorless,
       flavourless, insipid, savorless, savourless, vapid]
    9: lacking stimulating characteristics; uninteresting; "a bland
       little drama"; "a flat joke" [syn: bland, flat]
    10: having lost effervescence; "flat beer"; "a flat cola"
    11: sounded or spoken in a tone unvarying in pitch; "the owl's
        faint monotonous hooting" [syn: flat, monotone,
        monotonic, monotonous]
    12: horizontally level; "a flat roof"
    13: lacking the expected range or depth; not designed to give an
        illusion or depth; "a film with two-dimensional characters";
        "a flat two-dimensional painting" [syn: two-dimensional,
        2-dimensional, flat]
    14: not reflecting light; not glossy; "flat wall paint"; "a
        photograph with a matte finish" [syn: flat, mat, matt,
        matte, matted]
    15: commercially inactive; "flat sales for the month"; "prices
        remained flat"; "a flat market"
    n 1: a level tract of land; "the salt flats of Utah"
    2: a shallow box in which seedlings are started
    3: a musical notation indicating one half step lower than the
       note named
    4: freight car without permanent sides or roof [syn: flatcar,
       flatbed, flat]
    5: a deflated pneumatic tire [syn: flat, flat tire]
    6: scenery consisting of a wooden frame covered with painted
       canvas; part of a stage setting
    7: a suite of rooms usually on one floor of an apartment house
       [syn: apartment, flat]

Moby Thesaurus II by Grady Ward, 1.0:

892 Moby Thesaurus words for "flat":
   3-D, Pullman, Pullman car, abeyant, absolute, absolutely, absonant,
   accented, accidental, accommodation, accordant, accumbent,
   achromatic, achromic, act drop, admitting no exception, alabaster,
   alike, alkali flat, all-out, alluvial plain, alveolar, anemic,
   apace, apartment, apathetic, apical, apico-alveolar, apico-dental,
   arid, arrowlike, articulated, asbestos, asbestos board, ashen,
   ashy, assimilated, at full length, at full speed, at once, atonal,
   automatic, back, backdrop, baggage car, balanced, baldly, bank,
   bar, barren, barytone, basin, bated, batten, beat, betting house,
   betting parlor, bilabial, billiard table, blah, bland, blank,
   bled white, bloodless, bog, bony, border, boring, bottomland,
   bowling alley, bowling green, boxcar, brashly, brazenly, breve,
   broad, broke, bushveld, busted, caboose, cacophonous, cacuminal,
   cadaverous, campestral, campestrian, campo, car, carriage, casino,
   cataleptic, catatonic, categorical, categorically, central,
   cerebral, certain, chair car, chambers, champaign,
   champaign country, characterless, checked, chloranemic, clear,
   clerestory, close, cloth, coach, coal car, coastal plain, cold,
   cold-water flat, collapsed, colorless, common, commonplace,
   complete, completely, conclusive, consistent, consonant,
   consonantal, constant, continuant, continuous, coral reef,
   couchant, couche, coulisse, counterweight, covered waggon, cracked,
   crawling, creamy, crib, crotchet, crouched, cubic, curtain,
   curtain board, cyclorama, damped, dampened, day coach, dead,
   dead flat, dead level, dead straight, deadened, deadly pale,
   deathly pale, debased, decided, decisive, decor, decumbent,
   definite, definitely, definitive, deflated, delicate, delta,
   demisemiquaver, dental, depressed, desert, determinate, diaphonic,
   digs, dilute, diluted, dim, dimensional, dimmed, diner, dinghy,
   dingy, dining car, direct, directly, discolored, disconsonant,
   discordant, disharmonic, disharmonious, dismal, dissimilated,
   dissonant, dominant, dominant note, dopey, dormant, dorsal,
   double whole note, down, downright, downs, downy, drab, draggy,
   draped, drawing room, drearisome, dreary, drop, drop curtain, dry,
   dryasdust, dull, dulled, duplex, duplex apartment, dusty, earth,
   effete, eggshell, eighth note, elephantine, empty, enharmonic,
   enharmonic note, entire, entresol, equable, equal, esplanade,
   etiolated, even, evenly, exact, exactly, explicit, express,
   exsanguinated, exsanguine, exsanguineous, fade, faded, faint,
   fallow, featureless, fell, fen, final, fire curtain, firm,
   first floor, fixed, flat, flat broke, flat country, flat out,
   flat-chested, flat-out, flatcar, flatland, flatly, flats,
   flattened, flatways, flatwise, flavorless, fleshless, flipper,
   floor, flush, ford, forthwith, foul, fourth-dimensional, front,
   gambling den, gambling hall, gambling hell, gambling house,
   gaming house, gangling, gangly, garden apartment, gaunt, gawky,
   ghastly, glabrate, glabrescent, glabrous, glass, glide, global,
   gloss, glossal, glottal, gondola, grass veld, grassland, grating,
   gray, groggy, ground, ground floor, groveling, gruelly, guttural,
   haggard, half note, hanging, hard, harsh, heath, heavy, hell,
   hell for leather, hemidemisemiquaver, high, ho-hum, hollow,
   homaloid, homaloidal, homogeneous, horizontal, horizontal axis,
   horizontal fault, horizontal line, horizontal parallax,
   horizontal plane, horizontal projection, horizontally, hueless,
   humdrum, hypochromic, ice, immediately, immelodious, immutable,
   implicit, in a line, in abeyance, in suspense, inactive, inane,
   inappealable, indifferent, indisputable, indubitable, inert,
   inexcitable, inharmonic, inharmonious, insipid, intonated,
   invariable, iridescent, irrevocable, irrevocably, ivory, jejune,
   joint, knee-high, knocked flat, labial, labiodental, labiovelar,
   lackluster, laid low, lande, languid, languorous, lank, lanky,
   latent, lateral, lax, leaden, lean, lean-fleshed, lean-looking,
   ledge, leiotrichous, lengthways, lengthwise, level, level line,
   level plane, lifeless, light, like a shot, like greased lightning,
   lineal, linear, lingual, liquid, livid, living quarters, llano,
   local, lodgings, logy, lolling, lounging, low, low-built, low-hung,
   low-level, low-leveled, low-lying, low-set, low-spirited,
   low-statured, lowland, lowlands, luggage van, lunar mare, lurid,
   lusterless, lying, lying down, mahogany, mail car, mail van,
   marble, mare, marsh, mat, matte, matter-of-fact, meager, mealy,
   mean sea level, measured, mechanical, mellow, mesa, mesilla,
   methodic, mezzanine, mezzanine floor, mid, mild, milk-and-water,
   minim, monolithic, monophthongal, monotonous, moor, moorland,
   mother-of-pearl, muddy, muffled, mundane, musical note, musicless,
   muted, nacreous, narrow, nasal, nasalized, natural, neap, neutral,
   nonmelodious, note, occlusive, of a piece, off, off-key, off-tone,
   on a level, on the run, oofless, opalescent, open, open country,
   openly, ordered, orderly, ordinary, out of pitch, out of tone,
   out of tune, out-and-out, outright, outspread, outstretched,
   overthrown, oxytone, palace car, palatal, palatalized, pale,
   pale as death, pale-faced, pallid, pampa, pampas, pappy,
   parlor car, parterre, passenger car, passive, pastel, pasty,
   patent note, patinaed, pearly, pedestrian, peneplain, penthouse,
   peremptory, perfect, persistent, pharyngeal, pharyngealized,
   phlegmatic, phonemic, phonetic, phonic, pitch, pitched, plain,
   plainly, plains, plane, plateau, platform, playa, plodding,
   poetryless, pointless, poky, ponderous, poolroom, positive,
   positively, posttonic, prairie, prairies, precise, precisely,
   procumbent, prone, proportional, prosaic, prosing, prostrate,
   prosy, pulpy, punctured, quarter note, quaver, quickly, quiet, rag,
   railroad flat, railway car, rapidly, raucous, rawboned, reclining,
   rectilineal, rectilinear, recumbent, reef, reefer,
   refrigerator car, regular, rental, report, reposing,
   responding note, resupine, retroflex, rez-de-chaussee, right,
   robotlike, rolled, roomette, rooms, round, rounded, ruler-straight,
   runty, ruptured, sad, sallow, salt flat, salt marsh, salt pan,
   sandals, sandbank, sandbar, sapless, satin, savanna, savorless,
   scene, scenery, scraggy, scrawny, screen, sea level, sea of grass,
   sebkha, sedentary, semibreve, semigloss, semiquaver, semivowel,
   set of rooms, shallow, shallows, shaped note, sharp, shelf, shoal,
   shoal water, short, shrill, sickly, side scene, silk, simple,
   sixteenth note, sixty-fourth note, skeletal, skinny, slack,
   sleeper, sleeping, slide, slow, sluggish, slumbering, smoker,
   smoking car, smoldering, smooth, smooth-shaven, smooth-textured,
   smoothed out, smoothened, smothered, sober, soft, soft-colored,
   soft-hued, softened, solemn, somber, sonant, sordo, sour, space,
   space-time, spare, spatial, spatiotemporal, speedily, spherical,
   spiccato, spiceless, spidery, spindling, spindly, spiritless,
   sporting house, sprawled, sprawling, spread, spread out, squashed,
   squashed flat, squat, squatty, stable, staccato, stage screw,
   stagnant, stale, standard, standing, static, steadfast, steady,
   steppe, steppes, stereoscopic, sterile, stiff, stifled, stockcar,
   stodgy, stone-broke, stony, stooped, stopped, story, straight,
   straight-cut, straight-front, straight-out, straight-side, strand,
   strapped, streamlined, street floor, stressed, stretched out,
   strident, strong, studio, stuffy, stumpy, suave, subdued, subtle,
   suite, superficial, supine, surd, sure, surface, sustained note,
   swamp, sweet, swiftly, syllabic, systematic, tab, table, tableau,
   tableland, tabloid, tabular, tallow-faced, tame, tank, tasteless,
   teaser, tedious, tender, tenement, tennis court, tense, tercet,
   terrace, thick, thin, thin-bellied, thin-fleshed,
   thirty-second note, three-dimensional, throaty, tidal flats, tired,
   tiresome, tonal, tone, toneless, tonic, tormentor, torpid, total,
   transformation, transformation scene, tree veld, triplet, triplex,
   trodden, trodden flat, truck, true, tundra, tuneless, twangy,
   twiggy, two-dimensional, unaccented, unambiguous, unaroused,
   unbending, unbent, unbowed, unbroken, unchangeable, unchanged,
   unchanging, uncircumscribed, uncolored, uncompromisingly,
   unconditional, unconditioned, uncurved, undeflected, undersized,
   underweight, undeviating, undifferentiated, undistorted,
   undiversified, undoubting, unelevated, unembellished, unequivocal,
   unexciting, unflavored, unhampered, unharmonious, unhesitating,
   unidealistic, uniform, unimaginative, unimpassioned, uninteresting,
   uninterrupted, unlimited, unlively, unmelodious, unmistakable,
   unmitigated, unmodifiable, unmodified, unmusical, unpalatable,
   unpoetic, unpolished, unqualified, unquestionable, unquestioning,
   unrealistic, unreserved, unrestricted, unromantic, unrough,
   unroughened, unrounded, unruffled, unsavory, unshiny, unstressed,
   unswerving, untunable, untuned, untuneful, unturned, unvaried,
   unvarying, unwaivable, upland, upright, utter, utterly, van, vapid,
   vega, velar, veld, velvet, vertical, vocalic, vocoid, voiced,
   voiceless, volumetric, vowel, vowellike, waggon, wan, washed-out,
   washy, water level, watered, watered-down, watery, waxen, weak,
   weald, wetlands, whey-faced, white, whole, whole note, wholly,
   wide, wide-open spaces, wing, wingcut, wishy-washy, without delay,
   without exception, without reserve, wold, woodcut, wooden



The Jargon File (version 4.4.7, 29 Dec 2003):

flat
 adj.

    1. [common] Lacking any complex internal structure. ?That bitty box has
    only a flat filesystem, not a hierarchical one.? The verb form is flatten
    .

    2. Said of a memory architecture (like that of the VAX or 680x0) that is
    one big linear address space (typically with each possible value of a
    processor register corresponding to a unique core address), as opposed to a
    segmented architecture (like that of the 80x86) in which addresses are
    composed from a base-register/offset pair (segmented designs are generally
    considered cretinous).

    Note that sense 1 (at least with respect to filesystems) is usually used
    pejoratively, while sense 2 is a Good Thing.


The Free On-line Dictionary of Computing (30 December 2018):

flat

   1. Lacking any complex internal structure.  "That bitty box
   has only a flat file system, not a hierarchical one."  The verb
   form is flatten.  Usually used pejoratively (at least with
   respect to file systems).

   2. Said of a memory architecture like that of the VAX or
   Motorola 680x0 that is one big linear address space
   (typically with each possible value of a processor register
   corresponding to a unique address).  This is a Good Thing.
   The opposite is a "segmented" architecture like that of the
   Intel 80x86 in which addresses are composed from a
   base-register/offset pair.  Segmented designs are generally
   considered cretinous.

   3. A flat domain is one where all elements except bottom
   are incomparable (equally well defined).  E.g. the integers.

   [Jargon File]


U.S. Gazetteer Places (2000):

Flat, AK -- U.S. Census Designated Place in Alaska
   Population (2000):    4
   Housing Units (2000): 3
   Land area (2000):     161.068896 sq. miles (417.166508 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    161.068896 sq. miles (417.166508 sq. km)
   FIPS code:            25880
   Located within:       Alaska (AK), FIPS 02
   Location:             62.454135 N, 158.008284 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Flat, AK
    Flat