The Collaborative International Dictionary of English v.0.48:

Scrimshaw \Scrim"shaw`\, v. t.
   To ornament, as shells, ivory, etc., by engraving, and
   (usually) rubbing pigments into the incised lines. [Sailor's
   cant. U.S.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Scrimshaw \Scrim"shaw`\, n.
   A shell, a whale's tooth, or the like, that is scrimshawed.
   [Sailor's cant, U.S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

scrimshaw
    n 1: a carving (or engraving) on whalebone, whale ivory, walrus
         tusk, etc., usually by American whalers