The Collaborative International Dictionary of English v.0.48:

Tusk-shell \Tusk"-shell`\ (t[u^]sk"-sh[e^]l`), n. (Zool.)
   See 2d Tusk, n., 2.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tusk \Tusk\, n. [OE. tusk, the same word as tusch, AS. tusc. See
   Tush a tooth.]
   1. (Zool.) One of the elongated incisor or canine teeth of
      the wild boar, elephant, etc.; hence, any long, protruding
      tooth.
      [1913 Webster]

   2. (Zool.) A toothshell, or Dentalium; -- called also
      tusk-shell.
      [1913 Webster]

   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.
      [1913 Webster]