(1):

(n.) Any cirriped crustacean adhering to rocks, floating timber, ships, etc., esp. (a) the sessile species (genus Balanus and allies), and (b) the stalked or goose barnacles (genus Lepas and allies). See Cirripedia, and Goose barnacle.

(2):

(n.) A bernicle goose.

(3):

(n.) An instrument for pinching a horse's nose, and thus restraining him.

(4):

(sing.) Spectacles; - so called from their resemblance to the barnacles used by farriers.