Source : Webster's Revised Unabridged Dictionary (1913)

Nail \Nail\, n. [AS. n[ae]gel, 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. ?, Skr. nakha. ?]
   1. (Anat.) the horny scale of plate of epidermis at the end
      of the fingers and toes of man and many apes.

            His nayles like a briddes claws were. --Chaucer.

   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.

   2. (Zo["o]l.)
      (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.

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

   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.

Nail \Nail\, v. t. [imp. & p. p. {Nailed}; p. pr. & vb. n.
   {Nailing}.] [AS. n[ae]glian. 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.

            He is now dead, and nailed in his chest. --Chaucer.

   2. To stud or boss with nails, or as with nails.

            The rivets of your arms were nailed with gold.
                                                  --Dryden.

   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.

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

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

   {To nail} {a lie or an assertion}, 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.

Source : WordNet®

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

nail
     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}, {apprehend}, {arrest}, {pick up},
         {nab}, {cop}]
     3: hit hard; "He smashed a 3-run homer" [syn: {smash}, {boom},
        {blast}]
     4: succeed in obtaining a position; "He nailed down a spot at
        Harvard" [syn: {nail down}, {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}]
     6: locate exactly; "can you pinpoint the position of the
        enemy?"; "The chemists could not nail the identity of the
        chromosome" [syn: {pinpoint}]
     7: complete a pass [syn: {complete}]