Merriam-Webster Collegiate Dictionary - limpet

 noun  Etymology: Middle English lempet, from Old English lempedu, from Medieval Latin lampreda lamprey  Date: before 12th century  1. a marine gastropod mollusk (especially families Acmaeidae and Patellidae) that has a low conical shell broadly open beneath, browses over rocks or timbers in the littoral area, and clings very tightly when disturbed  2. one that clings tenaciously to someone or something  3. an explosive device designed to cling magnetically to a metallic surface (as the hull of a ship)