Source : Webster's Revised Unabridged Dictionary (1913)

Tusk \Tusk\, n. [OE. tusk, the same word as tusch, AS. tusc. See
   {Tush} a tooth.]
   1. (Zo["o]l.) One of the elongated incisor or canine teeth of
      the wild boar, elephant, etc.; hence, any long, protruding
      tooth.

   2. (Zo["o]l.) A toothshell, or Dentalium; -- called also
      {tusk-shell}.

   3. (Carp.) A projecting member like a tenon, and serving the
      same or a similar purpose, but composed of several steps,
      or offsets. Thus, in the illustration, a is the tusk, and
      each of the several parts, or offsets, is called a tooth.

Tusk \Tusk\, n. (Zo["o]l.)
   Same as {Torsk}.

Tusk \Tusk\, v. i.
   To bare or gnash the teeth. [Obs.]

Source : WordNet®

tusk
     n 1: a hard smooth ivory colored dentine that makes up most of
          the tusks of elephants and walruses [syn: {ivory}]
     2: a long pointed tooth specialized for fighting or digging;
        especially in an elephant or walrus or hog

tusk
     v 1: stab or pierce with a horn or tusk; "the rhino horned the
          explorer" [syn: {horn}]
     2: remove the tusks of animals; "tusk an elephant" [syn: {detusk}]