bar·na·cle / ˈbärnəkəl/ • n. a marine crustacean (class Cirripedia) with an external shell, which attaches itself permanently to a variety of surfaces. ∎  used figuratively to describe a tenacious person or thing. DERIVATIVES: bar·na·cled adj.

barnacle Crustacean that lives mostly on rocks and floating timber. Some barnacles live on whales, turtles and fish without being parasitic, although there are also parasitic species. The larvae swim freely until ready to become adults, when they settle permanently on their heads; their bodies become covered with calcareous plates. The adult uses its feathery appendages to scoop food into its mouth. Two main types are those with stalks (goose barnacles) and those without (acorn barnacles). Subclass Cirripedia.

barnacle wild goose Anas leucopsis XIII; marine crustacean XVI. ME. bernak, -ek(ke), corr, to medL. bernaca, -eca, whence app. F. barnache; barnacle(XV) corr. to F. barnacle, but may be of independent orig. ult. source unkn. The two meanings depend on an early belief that the goose was generated from a shellfish.