From Middle English barnakille, from earlier bernake, bernekke, from Old French bernaque (“barnacle”), from Gaulish *barenica (“limpet”) (compare Welsh brennig, Irish báirneac), from *barenos (“rock”) (compare Old Irish barenn (“boulder”)); for sense development, compare Ancient Greek λέπας (lépas, “rock”) which gave λεπάς (lepás, “limpet”).
barnacle (plural barnacles)
- A marine crustacean of the subclass Cirripedia that attaches itself to submerged surfaces such as tidal rocks or the bottoms of ships.
- The barnacle goose.
- (engineering, slang) In electrical engineering, a change made to a product on the manufacturing floor that was not part of the original product design.
- (computing, slang) On printed circuit boards, a change such as soldering a wire in order to connect two points, or addition such as an added resistor or capacitor, subassembly or daughterboard.
- (obsolete) An instrument like a pair of pincers, to fix on the nose of a vicious horse while shoeing so as to make it more tractable.
- (archaic, UK) A nickname for spectacles.
- (slang, obsolete) A good job, or snack easily obtained.
Related terms 
- To connect with or attach.
- To press close against something.
See also 
- barnacle in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913
- 1811 Dictionary of Vulgar Tongue, available from Project Gutenberg