Past tense of crow; made the loud cry of a rooster, or boasted loudly and triumphantly about something.
From Old English 'crawan,' the crow's cry being imitative in origin, resembling the actual sound. The metaphorical sense (to boast) developed naturally from the rooster's loud, proud call.
The word 'crow' is onomatopoeia—it literally sounds like what it describes—and that's why people adopted it for boasting: there's something inherently proud and loud about the sound itself.
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