Silky protective cases that caterpillars spin around themselves before transforming into butterflies or moths.
From French 'cocon,' derived from Spanish or Portuguese 'coco' (coconut, from the coconut-like shape). The resemblance to coconuts led sailors and traders to use that word for the silk-wrapped structures.
It's wild that cocoons got their name because someone thought they looked like coconuts—two totally unrelated tropical things. Medieval traders saw a silky shell and said 'that's like a coco!' That's how language works: resemblance becomes the name, and you're stuck with it forever.
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