cheerful, happy, and lively in attitude; sounding bright and energetic like a bird's song.
From 'chirp' (the sound birds make) + '-y' (adjective suffix). First used in the early 1800s to describe people with bird-like cheerfulness.
We literally borrowed from birds to describe happiness! Other emotions have animal origins too ('pig-headed,' 'eagle-eyed'), but 'chirpy' is special because birds that chirp are everywhere and universally seen as innocent and joyful.
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