The Collaborative International Dictionary of English v.0.48:

Shipworm \Ship"worm`\, n. (Zool.)
   Any long, slender, worm-shaped bivalve mollusk of Teredo
   and allied genera. The shipworms burrow in wood, and are
   destructive to wooden ships, piles of wharves, etc. See
   Teredo.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Teredo \Te*re"do\, n.; pl. E. Teredos, L. Teredines. [L., a
   worm that gnaws wood, clothes, etc.; akin to Gr. ?, L. terere
   to rub.] (Zool.)
   A genus of long, slender, wormlike bivalve mollusks which
   bore into submerged wood, such as the piles of wharves,
   bottoms of ships, etc.; -- called also shipworm. See
   Shipworm. See Illust. in Appendix.
   [1913 Webster]

WordNet (r) 3.0 (2006):

shipworm
    n 1: wormlike marine bivalve that bores into wooden piers and
         ships by means of drill-like shells [syn: shipworm,
         teredinid]