Past tense of cuckoo; to repeatedly call out 'cuckoo' like a cuckoo bird, or to deceive someone by replacing their partner.
From Old English 'cuc' (imitative of the bird's call) + the past tense suffix '-ed'. The sense of 'deceive' comes from the cuckoo's habit of laying eggs in other birds' nests, metaphorically applied to sexual betrayal.
The cuckoo bird is basically nature's con artist—it tricks other birds into raising its babies, and this sneaky behavior became so famous that European languages borrowed it as slang for 'cheated spouse' and general deception.
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