(1):

(n.) One that bores; an instrument for boring.

(2):

(n.) A marine, bivalve mollusk, of the genus Teredo and allies, which burrows in wood. See Teredo.

(3):

(n.) Any bivalve mollusk (Saxicava, Lithodomus, etc.) which bores into limestone and similar substances.

(4):

(n.) One of the larvae of many species of insects, which penetrate trees, as the apple, peach, pine, etc. See Apple borer, under Apple.

(5):

(n.) The hagfish (Myxine).