1. Any of various marine crustaceans of the subclass Cirripedia that in the adult stage form a hard shell which remains attached to submerged surfaces such as rocks and ships' hulls, and that have feathery appendages used for filter feeding.
2. The barnacle goose.
[Middle English, barnacle goose, from Old French bernacle, from Medieval Latin bernacula, diminutive of bernaca, of unknown origin.]
Word History: The word barnacle is known from as far back as the early 13th century. At that time it did not refer to the crustacean, as it does today, but only to the species of waterfowl now more often known as the barnacle goose; more than 300 years went by before barnacle was used to refer to the crustacean. One might well wonder what the connection between these two creatures is. The answer lies in natural history. Until fairly recent times, it was widely believed that certain animals were engendered spontaneously from particular substances. Maggots, for instance, were believed to be generated from rotting meat. Because the barnacle goose breeds in the Arctic, no one at that time had ever witnessed the bird breeding; as a result, it was thought to be spontaneously generated from trees along the shore, or from rotting wood. Wood that has been in the ocean for any length of time is often dotted with barnacles, and it was natural for people to believe that the crustaceans were also engendered directly from the wood, like the geese. In fact, as different as the two creatures might appear to us, they share a similar trait: barnacles have long feathery cirri that are reminiscent of a bird's plumage. This led one writer in 1678 to comment on the "multitudes of little Shells; having within them little Birds perfectly shap'd, supposed to be Barnacles [that is, barnacle geese]." In popular conception the two creatures were thus closely linked. Over time the crustacean became the central referent of the word, and the bird was called the barnacle goose for clarity, making barnacle goose an early example of what we now call a retronym.
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