one that bores; an instrument for boring.-a marine, bivalve mollusk, of the genus teredo and allies, which burrows in wood. see teredo.-any bivalve mollusk (saxicava, lithodomus, etc.) which bores into limestone and similar substances.-one of the larvae of many species of insects, which penetrate trees, as the apple, peach, pine, etc. see apple borer, under apple.-the hagfish (myxine).