The Collaborative International Dictionary of English v.0.48:

Hair \Hair\ (h[^a]r), n. [OE. her, heer, h[ae]r, AS. h[=ae]r;
   akin to OFries. h[=e]r, D. & G. haar, OHG. & Icel. h[=a]r,
   Dan. haar, Sw. h[*a]r; cf. Lith. kasa.]
   1. The collection or mass of filaments growing from the skin
      of an animal, and forming a covering for a part of the
      head or for any part or the whole of the body.
      [1913 Webster]

   2. One the above-mentioned filaments, consisting, in
      vertebrate animals, of a long, tubular part which is free
      and flexible, and a bulbous root imbedded in the skin.
      [1913 Webster]

            Then read he me how Sampson lost his hairs.
                                                  --Chaucer.
      [1913 Webster]

            And draweth new delights with hoary hairs.
                                                  --Spenser.
      [1913 Webster]

   3. Hair (human or animal) used for various purposes; as, hair
      for stuffing cushions.
      [1913 Webster]

   4. (Zool.) A slender outgrowth from the chitinous cuticle of
      insects, spiders, crustaceans, and other invertebrates.
      Such hairs are totally unlike those of vertebrates in
      structure, composition, and mode of growth.
      [1913 Webster]

   5. (Bot.) An outgrowth of the epidermis, consisting of one or
      of several cells, whether pointed, hooked, knobbed, or
      stellated. Internal hairs occur in the flower stalk of the
      yellow frog lily (Nuphar).
      [1913 Webster]

   6. A spring device used in a hair-trigger firearm.
      [1913 Webster]

   7. A haircloth. [Obs.] --Chaucer.
      [1913 Webster]

   8. Any very small distance, or degree; a hairbreadth.
      [1913 Webster]

   Note: Hairs is often used adjectively or in combination; as,
         hairbrush or hair brush, hair dye, hair oil, hairpin,
         hair powder, a brush, a dye, etc., for the hair.
         [1913 Webster]

   Against the hair, in a rough and disagreeable manner;
      against the grain. [Obs.] "You go against the hair of your
      professions." --Shak.

   Hair bracket (Ship Carp.), a molding which comes in at the
      back of, or runs aft from, the figurehead.

   Hair cells (Anat.), cells with hairlike processes in the
      sensory epithelium of certain parts of the internal ear.


   Hair compass, Hair divider, a compass or divider capable
      of delicate adjustment by means of a screw.

   Hair glove, a glove of horsehair for rubbing the skin.

   Hair lace, a netted fillet for tying up the hair of the
      head. --Swift.

   Hair line, a line made of hair; a very slender line.

   Hair moth (Zool.), any moth which destroys goods made of
      hair, esp. Tinea biselliella.

   Hair pencil, a brush or pencil made of fine hair, for
      painting; -- generally called by the name of the hair
      used; as, a camel's hair pencil, a sable's hair pencil,
      etc.

   Hair plate, an iron plate forming the back of the hearth of
      a bloomery fire.

   Hair powder, a white perfumed powder, as of flour or
      starch, formerly much used for sprinkling on the hair of
      the head, or on wigs.

   Hair seal (Zool.), any one of several species of eared
      seals which do not produce fur; a sea lion.

   Hair seating, haircloth for seats of chairs, etc.

   Hair shirt, a shirt, or a band for the loins, made of
      horsehair, and worn as a penance.

   Hair sieve, a strainer with a haircloth bottom.

   Hair snake. See Gordius.

   Hair space (Printing), the thinnest metal space used in
      lines of type.

   Hair stroke, a delicate stroke in writing.

   Hair trigger, a trigger so constructed as to discharge a
      firearm by a very slight pressure, as by the touch of a
      hair. --Farrow.

   Not worth a hair, of no value.

   To a hair, with the nicest distinction.

   To split hairs, to make distinctions of useless nicety.
      [1913 Webster] hairball

WordNet (r) 3.0 (2006):

hair
    n 1: a covering for the body (or parts of it) consisting of a
         dense growth of threadlike structures (as on the human
         head); helps to prevent heat loss; "he combed his hair";
         "each hair consists of layers of dead keratinized cells"
    2: a very small distance or space; "they escaped by a
       hair's-breadth"; "they lost the election by a whisker" [syn:
       hair's-breadth, hairsbreadth, hair, whisker]
    3: filamentous hairlike growth on a plant; "peach fuzz" [syn:
       hair, fuzz, tomentum]
    4: any of the cylindrical filaments characteristically growing
       from the epidermis of a mammal; "there is a hair in my soup"
       [syn: hair, pilus]
    5: cloth woven from horsehair or camelhair; used for upholstery
       or stiffening in garments [syn: haircloth, hair]
    6: a filamentous projection or process on an organism

Moby Thesaurus II by Grady Ward, 1.0:

190 Moby Thesaurus words for "hair":
   a continental, a curse, a damn, a darn, a hoot, ace, animal fiber,
   artificial fiber, atom, bagatelle, bauble, bean, bibelot, bit,
   bowshot, braids, brass farthing, brief span, bristle, button,
   cambric tea, capillament, cent, cilium, cirrus, close quarters,
   close range, closeness, coat, cobweb, confinement, crack,
   crowdedness, curio, dab, denier, dishwater, dole, dot, dram,
   dribble, driblet, dwarf, earreach, earshot, farce, farthing,
   feather, fiber, fibrilla, fig, filament, filamentule, flagellum,
   fleabite, fleck, fleece, flyspeck, folderol, fraction, fragment,
   fribble, frippery, fur, gaud, gewgaw, gimcrack, gobbet, gossamer,
   grain, granule, groat, gruel, gunshot, hair space, hairbreadth,
   hairsbreadth, halfpenny, handful, hank, hill of beans, horsehair,
   house of cards, incapaciousness, inch, incommodiousness, iota,
   jest, joke, jot, kickshaw, knickknack, knickknackery, limitation,
   little, little bit, little ways, locks, mane, matchwood,
   milk and water, minikin, minim, minimum, minutiae, mite, mockery,
   modicum, molecule, molehill, mote, narrow gauge, narrowness,
   nearness, nutshell, ounce, particle, pebble, pelt, peppercorn,
   picayune, pile, pin, pinch, pinch of snuff, pinprick, pistol shot,
   pittance, point, pubescence, pubic hair, rap, red cent, reed,
   restrictedness, restriction, rope of sand, row of pins, rush,
   sand castle, scruple, setula, shag, shit, short distance,
   short piece, short way, skein, slenderness, smidgen, smitch, snap,
   sneeshing, sou, span, speck, spitting distance, spoonful, spot,
   step, straitness, strand, straw, strictness, suture, tendril,
   thimbleful, thread, threadlet, tight squeeze, tightness, tiny bit,
   tittle, toy, trace, tresses, trifle, trifling amount, trinket,
   trivia, triviality, tuppence, two cents, twopence, water, web,
   whim-wham, whisker, whit, wool



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

hair
 n.

    [back-formation from hairy] The complications that make something hairy.
    ?Decoding TECO commands requires a certain amount of hair.? Often seen in
    the phrase infinite hair, which connotes extreme complexity. Also in
    hairiferous (tending to promote hair growth): ?GNUMACS elisp encourages
    lusers to write complex editing modes.? ?Yeah, it's pretty hairiferous all
    right.? (or just: ?Hair squared!?)


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

hair

   [back-formation from hairy] The complications that make
   something hairy.  "Decoding TECO commands requires a certain
   amount of hair."  Often seen in the phrase "infinite hair",
   which connotes extreme complexity.  Also in "hairiferous"
   (tending to promote hair growth): "GNUMACS elisp encourages
   lusers to write complex editing modes."  "Yeah, it's pretty
   hairiferous all right." (Or just: "Hair squared!")


Easton's 1897 Bible Dictionary:

Hair
   (1.) The Egyptians let the hair of their head and beard grow
   only when they were in mourning, shaving it off at other times.
   "So particular were they on this point that to have neglected it
   was a subject of reproach and ridicule; and whenever they
   intended to convey the idea of a man of low condition, or a
   slovenly person, the artists represented him with a beard."
   Joseph shaved himself before going in to Pharoah (Gen. 41:14).
   The women of Egypt wore their hair long and plaited. Wigs were
   worn by priests and laymen to cover the shaven skull, and false
   beards were common. The great masses of hair seen in the
   portraits and statues of kings and priests are thus altogether
   artificial.

     (2.) A precisely opposite practice, as regards men, prevailed
   among the Assyrians. In Assyrian sculptures the hair always
   appears long, and combed closely down upon the head. The beard
   also was allowed to grow to its full length.

     (3.) Among the Greeks the custom in this respect varied at
   different times, as it did also among the Romans. In the time of
   the apostle, among the Greeks the men wore short hair, while
   that of the women was long (1 Cor. 11:14, 15). Paul reproves the
   Corinthians for falling in with a style of manners which so far
   confounded the distinction of the sexes and was hurtful to good
   morals. (See, however, 1 Tim. 2:9, and 1 Pet. 3:3, as regards
   women.)

     (4.) Among the Hebrews the natural distinction between the
   sexes was preserved by the women wearing long hair (Luke 7:38;
   John 11:2; 1 Cor. 11:6), while the men preserved theirs as a
   rule at a moderate length by frequent clipping.

     Baldness disqualified any one for the priest's office (Lev.
   21).

     Elijah is called a "hairy man" (2 Kings 1:8) from his flowing
   locks, or more probably from the shaggy cloak of hair which he
   wore. His raiment was of camel's hair.

     Long hair is especially noticed in the description of
   Absalom's person (2 Sam. 14:26); but the wearing of long hair
   was unusual, and was only practised as an act of religious
   observance by Nazarites (Num. 6:5; Judg. 13:5) and others in
   token of special mercies (Acts 18:18).

     In times of affliction the hair was cut off (Isa. 3:17, 24;
   15:2; 22:12; Jer. 7:29; Amos 8:10). Tearing the hair and letting
   it go dishevelled were also tokens of grief (Ezra 9:3). "Cutting
   off the hair" is a figure of the entire destruction of a people
   (Isa. 7:20). The Hebrews anointed the hair profusely with
   fragrant ointments (Ruth 3:3; 2 Sam. 14:2; Ps. 23:5; 45:7,
   etc.), especially in seasons of rejoicing (Matt. 6:17; Luke
   7:46).