The Collaborative International Dictionary of English v.0.48:
Barnacle \Bar"na*cle\, n. [Prob. from E. barnacle a kind of
goose, which was popularly supposed to grow from this
shellfish; but perh. from LL. bernacula for pernacula, dim.
of perna ham, sea mussel; cf. Gr. pe`rna ham. Cf. F.
bernacle, barnacle, E. barnacle a goose; and Ir. bairneach,
barneach, limpet.] (Zool.)
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.
Barnacle eater (Zool.), the orange filefish.
Barnacle scale (Zool.), a bark louse (Ceroplastes
cirripediformis) of the orange and quince trees in
Florida. The female scale curiously resembles a sessile
barnacle in form.