The Collaborative International Dictionary of English v.0.48:

Nail \Nail\ (n[=a]l), n. [AS. naegel, akin to D. nagel, OS. &
   OHG. nagal, G. nagel, Icel. nagl, nail (in sense 1), nagli
   nail (in sense 3), Sw. nagel nail (in senses 1 and 3), Dan.
   nagle, Goth. ganagljan to nail, Lith. nagas nail (in sense
   1), Russ. nogote, L. unguis, Gr. "o`nyx, Skr. nakha.
   [root]259.]
   1. (Anat.) the horny scale of plate of epidermis at the end
      of the fingers and toes of man and many apes.
      [1913 Webster]

            His nayles like a briddes claws were. --Chaucer.
      [1913 Webster]

   Note: The nails are strictly homologous with hoofs and claws.
         When compressed, curved, and pointed, they are called
         talons or claws, and the animal bearing them is
         said to be unguiculate; when they incase the
         extremities of the digits they are called hoofs, and
         the animal is ungulate.
         [1913 Webster]

   2. (Zool.)
      (a) The basal thickened portion of the anterior wings of
          certain hemiptera.
      (b) The terminal horny plate on the beak of ducks, and
          other allied birds.
          [1913 Webster]

   3. A slender, pointed piece of metal, usually with a head[2],
      used for fastening pieces of wood or other material
      together, by being driven into or through them.
      [1913 Webster]

   Note: The different sorts of nails are named either from the
         use to which they are applied, from their shape, from
         their size, or from some other characteristic, as
         shingle, floor, ship-carpenters', and horseshoe nails,
         roseheads, diamonds, fourpenny, tenpenny (see Penny,
         a.), chiselpointed, cut, wrought, or wire nails, etc.
         [1913 Webster]

   4. A measure of length, being two inches and a quarter, or
      the sixteenth of a yard.
      [1913 Webster]

   Nail ball (Ordnance), a round projectile with an iron bolt
      protruding to prevent it from turning in the gun.

   Nail plate, iron in plates from which cut nails are made.


   On the nail, in hand; on the spot; immediately; without
      delay or time of credit; as, to pay money on the nail; to
      pay cash on the nail. "You shall have ten thousand pounds
      on the nail." --Beaconsfield.

   To hit the nail on the head,
      (a) to hit most effectively; to do or say a thing in the
          right way.
      (b) to describe the most important factor.
          [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Nail \Nail\, v. t. [imp. & p. p. Nailed (n[=a]ld); p. pr. &
   vb. n. Nailing.] [AS. naeglian. See Nail, n.]
   1. To fasten with a nail or nails; to close up or secure by
      means of nails; as, to nail boards to the beams.
      [1913 Webster]

            He is now dead, and nailed in his chest. --Chaucer.
      [1913 Webster]

   2. To stud or boss with nails, or as with nails.
      [1913 Webster]

            The rivets of your arms were nailed with gold.
                                                  --Dryden.
      [1913 Webster]

   3. To fasten, as with a nail; to bind or hold, as to a
      bargain or to acquiescence in an argument or assertion;
      hence, to catch; to trap.
      [1913 Webster]

            When they came to talk of places in town, you saw at
            once how I nailed them.               --Goldsmith.
      [1913 Webster]

   4. To spike, as a cannon. [Obs.] --Crabb.
      [1913 Webster]

   To nail an assertion or To nail a lie, etc., to detect
      and expose it, so as to put a stop to its currency; -- an
      expression probably derived from the former practice of
      shopkeepers, who were accustomed to nail bad or
      counterfeit pieces of money to the counter.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nail
    n 1: horny plate covering and protecting part of the dorsal
         surface of the digits
    2: a thin pointed piece of metal that is hammered into materials
       as a fastener
    3: a former unit of length for cloth equal to 1/16 of a yard
    v 1: attach something somewhere by means of nails; "nail the
         board onto the wall"
    2: take into custody; "the police nabbed the suspected
       criminals" [syn: collar, nail, apprehend, arrest,
       pick up, nab, cop]
    3: hit hard; "He smashed a 3-run homer" [syn: smash, nail,
       boom, blast]
    4: succeed in obtaining a position; "He nailed down a spot at
       Harvard" [syn: nail down, nail, peg]
    5: succeed at easily; "She sailed through her exams"; "You will
       pass with flying colors"; "She nailed her astrophysics
       course" [syn: breeze through, ace, pass with flying
       colors, sweep through, sail through, nail]
    6: locate exactly; "can you pinpoint the position of the
       enemy?"; "The chemists could not nail the identity of the
       chromosome" [syn: pinpoint, nail]
    7: complete a pass [syn: complete, nail]

Moby Thesaurus II by Grady Ward, 1.0:

187 Moby Thesaurus words for "nail":
   Gibraltar, abduct, adamant, agonize, articulate, at once, attach,
   bag, batten, batten down, be correct, be precise, be right, biff,
   bolt, bone, brick, buckle, butt, button, cabbage, capture,
   carry off, catch, cement, chafe, clasp, claw, claws, cleat, clench,
   clinch, clip, clout, clutch, clutches, cold, collar, complete,
   conclude, concrete, diamond, digits, ding, distinguish, dovetail,
   enmesh, ensnare, entangle, entrap, fangs, fasten, fastener,
   fastening, finalize, fingernails, fingers, fix, flint, focus, foul,
   fret, get, glue, grab, granite, grapple, hands, hard as nails,
   hardy, harpoon, hasp, have, heart of oak, hinge, hit, hitch, hook,
   hooks, horse, identify, immediately, iron, jam, jaws, join, joint,
   kidnap, know, know again, land, lasso, latch, lion, lock, make out,
   mandibles, marble, maxillae, meathooks, mesh, miter, mitts,
   mortise, nab, nail down, nails, net, nick, nip, nippers, noose,
   oak, on the nail, on the spot, ox, palm, peg, pin, pincers, pinch,
   place, pounces, prehend, promptly, punch, rabbet, realize,
   recall knowledge of, recognize, reidentify, resolve, right away,
   rivet, rock, rope, sack, scarf, screw, secure, settle, sew,
   shanghai, shoot, skewer, slog, slosh, snag, snap, snare, snatch,
   sniggle, sock, spear, spike, spot, staple, steel, stew over, stick,
   stitch, stone, strike, suffer, tack, take, talon, talons, tangle,
   tangle up with, teeth, tell, throttle, toggle, tough, trap,
   unfeeling, unguals, ungulae, unsentimental, unsympathetic,
   vigorous, wedge, whack, without delay, worry, zipper



Easton's 1897 Bible Dictionary:

Nail
   for fastening. (1.) Hebrew yathed, "piercing," a peg or nail of
   any material (Ezek. 15:3), more especially a tent-peg (Ex.
   27:19; 35:18; 38:20), with one of which Jael (q.v.) pierced the
   temples of Sisera (Judg. 4:21, 22). This word is also used
   metaphorically (Zech. 10:4) for a prince or counsellor, just as
   "the battle-bow" represents a warrior.

     (2.) Masmer, a "point," the usual word for a nail. The words
   of the wise are compared to "nails fastened by the masters of
   assemblies" (Eccl. 12:11, A.V.). The Revised Version reads, "as
   nails well fastened are the words of the masters," etc. Others
   (as Plumptre) read, "as nails fastened are the masters of
   assemblies" (comp. Isa. 22:23; Ezra 9:8). David prepared nails
   for the temple (1 Chr. 22:3; 2 Chr. 3:9). The nails by which our
   Lord was fixed to the cross are mentioned (John 20:25; Col.
   2:14).

     Nail of the finger (Heb. tsipporen, "scraping"). To "pare the
   nails" is in Deut. 21:12 (marg., "make," or "dress," or "suffer
   to grow") one of the signs of purification, separation from
   former heathenism (comp. Lev. 14:8; Num. 8:7). In Jer. 17:1 this
   word is rendered "point."


Bouvier's Law Dictionary, Revised 6th Ed (1856):

NAIL, A measure of length, equal to two inches and a quarter. Vide Measure.