The Collaborative International Dictionary of English v.0.48:

Barnacle \Bar"na*cle\, n. [See Bernicle.]
   A bernicle goose.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Barnacle \Bar"na*cle\, n. [OE. bernak, bernacle; cf. OF. bernac,
   and Prov. F. (Berri) berniques, spectacles.]
   1. pl. (Far.) An instrument for pinching a horse's nose, and
      thus restraining him.

   Note: [Formerly used in the sing.]
         [1913 Webster]

               The barnacles . . . give pain almost equal to
               that of the switch.                --Youatt.
         [1913 Webster]

   2. pl. Spectacles; -- so called from their resemblance to the
      barnacles used by farriers. [Cant, Eng.] --Dickens.
      [1913 Webster]

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.
       [1913 Webster]

   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bernicle \Ber"ni*cle\, n. [OE. bernak, bernacle; cf. OF. bernac;
   prob. fr. LL. bernacula for hibernicula, bernicula, fr.
   Hibernia; the birds coming from Hibernia or Ireland. Cf. 1st
   Barnacle.]
   A bernicle goose. [Written also barnacle.]
   [1913 Webster]

   Bernicle goose (Zool.), a goose (Branta leucopsis), of
      Arctic Europe and America. It was formerly believed that
      it hatched from the cirripeds of the sea (Lepas), which
      were, therefore, called barnacles, goose barnacles, or
      Anatifers. The name is also applied to other related
      species. See Anatifa and Cirripedia.
      [1913 Webster]

WordNet (r) 3.0 (2006):

barnacle
    n 1: marine crustaceans with feathery food-catching appendages;
         free-swimming as larvae; as adults form a hard shell and
         live attached to submerged surfaces [syn: barnacle,
         cirriped, cirripede]
    2: European goose smaller than the brant; breeds in the far
       north [syn: barnacle goose, barnacle, Branta leucopsis]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "barnacle":
   adherent, adhesive, beat, bloodsucker, bramble, brier, bulldog,
   burr, cement, deadbeat, decal, decalcomania, freeloader, glue,
   gunk, hanger-on, leech, limpet, lounge lizard, molasses, mucilage,
   parasite, paste, plaster, prickle, remora, smell-feast, spiv,
   sponge, sponger, sticker, sucker, syrup, thorn