A gray and black bird known for laying its eggs in other birds' nests, or slang for someone who is crazy or silly.
From Middle English 'cuckowe,' an imitative word echoing the bird's distinctive two-note call 'cuck-oo.' The word appears in multiple European languages with similar sound patterns. The slang meaning developed because cuckoos' parasitic breeding behavior seemed bizarre to people, eventually meaning 'crazy.'
The cuckoo's reputation got so weird that it became an insult—the bird doesn't raise its own babies, it tricks other birds into doing it, which Victorian people found deeply immoral and thus associated with craziness. Also, the bird gave us the cuckoo clock, one of the most charming musical inventions!
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