The Collaborative International Dictionary of English v.0.48:

Mat \Mat\, v. t. [imp. & p. p. Matted; p. pr. & vb. n.
   Matting.]
   1. To cover or lay with mats. --Evelyn.
      [1913 Webster]

   2. To twist, twine, or felt together; to interweave into, or
      like, a mat; to entangle.
      [1913 Webster]

            And o'er his eyebrows hung his matted hair.
                                                  --Dryden.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mat \Mat\ (m[a^]t), n. [Cf. Matte.]
   A name given by coppersmiths to an alloy of copper, tin,
   iron, etc., usually called white metal. [Written also
   matt.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mat \Mat\, a. [OF. See 4th Mate.]
   Cast down; dejected; overthrown; slain. [Obs.]
   [1913 Webster]

         When he saw them so piteous and so maat. --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mat \Mat\, v. i.
   To grow thick together; to become interwoven or felted
   together like a mat, as hair when wetted with a sticky
   substance; as, a long-haired cat whose fur is matted.
   [1913 Webster +PJC] Matabele

The Collaborative International Dictionary of English v.0.48:

Mat \Mat\, n. [AS. matt, meatt, fr. L. matta a mat made of
   rushes.]
   1. A thick flat fabric of sedge, rushes, flags, husks, straw,
      hemp, or similar material, placed on the floor and used
      for wiping and cleaning shoes at the door, for covering
      the floor of a hall or room to protect its surface, and
      for other purposes.
      [1913 Webster +PJC]

   2. Any similar flat object made of fabric or other material,
      such as rubber or plastic, placed flat on a surface for
      various uses, as for covering plant houses, putting
      beneath dishes or lamps on a table, securing rigging from
      friction, and the like.
      [1913 Webster +PJC]

   3. Anything growing thickly, or closely interwoven, so as to
      resemble a mat in form or texture; as, a mat of weeds; a
      mat of hair.
      [1913 Webster]

   4. An ornamental border made of paper, pasterboard, metal,
      etc., put under the glass which covers a framed picture;
      as, the mat of a daguerreotype.
      [1913 Webster]

   Mat grass. (Bot.)
      (a) A low, tufted, European grass (Nardus stricta).
      (b) Same as Matweed.

   Mat rush (Bot.), a kind of rush (Scirpus lacustris) used
      in England for making mats.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mat
    adj 1: not reflecting light; not glossy; "flat wall paint"; "a
           photograph with a matte finish" [syn: flat, mat,
           matt, matte, matted]
    n 1: a thick flat pad used as a floor covering
    2: mounting consisting of a border or background for a picture
       [syn: mat, matting]
    3: sports equipment consisting of a piece of thick padding on
       the floor for gymnastic sports [syn: mat, gym mat]
    4: a mass that is densely tangled or interwoven; "a mat of weeds
       and grass"
    5: a master's degree in teaching [syn: Master of Arts in
       Teaching, MAT]
    6: the property of having little or no contrast; lacking
       highlights or gloss [syn: flatness, lusterlessness,
       lustrelessness, mat, matt, matte]
    7: a small pad of material that is used to protect surface from
       an object placed on it
    v 1: twist together or entwine into a confusing mass; "The child
         entangled the cord" [syn: entangle, tangle, mat,
         snarl] [ant: disentangle, straighten out, unsnarl]
    2: change texture so as to become matted and felt-like; "The
       fabric felted up after several washes" [syn: felt, felt
       up, mat up, matt-up, matte up, matte, mat]

Moby Thesaurus II by Grady Ward, 1.0:

214 Moby Thesaurus words for "mat":
   achromatic, achromic, agora, air mattress, amphitheater, anemic,
   arena, ashen, ashy, athletic field, auditorium, background,
   barrier, bear garden, bedding, bled white, blind, bloodless,
   bolster, bowl, boxing ring, braid, brattice, buffer, buffer state,
   bulkhead, bull ring, bumper, cadaverous, campus, canvas, carpet,
   carpeting, chloranemic, circus, cloison, cockpit, coliseum,
   collision mat, colorless, colosseum, course, crop, cushion, dead,
   deaden, deadened, deadly pale, deathly pale, diaphragm, dim,
   dimmed, dingy, discolored, dissepiment, dividing line,
   dividing wall, division, doormat, drab, drop cloth, duckboards,
   dull, enlace, entwine, etiolated, exsanguinated, exsanguine,
   exsanguineous, faded, faint, fallow, fender, field, flat, fleece,
   floor, floorboards, flooring, forum, ghastly, gray, ground,
   ground cloth, ground-sheet, gym, gymnasium, haggard, hall, head,
   head of hair, hippodrome, hueless, hypochromic,
   innerspring mattress, interknit, interlace, interseptum, intertie,
   intertissue, intertwine, intertwist, interweave, intort, knit,
   lace, lackluster, leaden, lifeless, lists, locale, locks, loom,
   loop, lurid, lusterless, mane, marketplace, mattress, mealy,
   midriff, midsection, milieu, mop, muddy, muted, net, neutral,
   noose, open forum, pad, palaestra, pale, pale as death, pale-faced,
   pallet, pallid, panel, parade ground, paries, partition,
   party wall, pasty, pave, pavement, pillow, pit, place, plait,
   platform, pleach, precinct, prize ring, property line,
   public square, purlieu, raddle, range, ring, rug, sallow, scene,
   scene of action, scenery, separation, septulum, septum, setting,
   shag, shock, shock pad, sickly, site, sleeping bag, somber, sphere,
   splice, springs, squared circle, stadium, stage, stage set,
   stage setting, tallow-faced, terrain, thatch, theater, tiling,
   tilting ground, tiltyard, tissue, tone down, toneless, tresses,
   twill, twine, twist, uncolored, underbed, underbedding, walk, wall,
   wan, washed-out, wattle, waxen, weak, weave, web, welcome mat,
   whey-faced, white, wreathe, wrestling ring