/ ˈbɑːnəkl; NAmE ˈbɑːrn-/ noun
a small shellfish that attaches itself to objects underwater, for example to rocks and the bottoms of ships
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WORD ORIGIN
late 16th cent.: from medieval Latin bernaca , of unknown origin. In Middle English the term denoted the barnacle goose, whose breeding grounds were then unknown and which was thought to hatch from the shell of the crustacean to which it gave its name.