1. (Science: zoology) Any cirriped marine crustacean free swimming in the larval state, but permanently fixed as adults, adhering to rocks, floating timber, ships, etc.
there are some 800 described species, grouped in several genera, including lepas, balanus, scalpellum, and the stalked or goose barnacles (genus lepas and allies).
2. (Science: zoology) barnacle eater, a bark louse (Ceroplastes cirripediformis) of the orange and quince trees in Florida. The female scale curiously resembles a sessile barnacle in form.
3. (Science: veterinary) An instrument for pinching a horses nose, and thus restraining him.
4. Spectacles; so called from their resemblance to the barnacles used by farriers.
Origin: Prob. From E. Barnacle a kind of goose, which was popularly supposed to grow from this shellfish.