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A song that gets stuck in your head without prompting. Also, any opportunity to break out randomly into song. Often related to an earworm
I found myself spontuneously humming "Piece by Piece" under my breath.

When I complained that it was "hot in here," my friend spontuneously sang "so take off all your clothes..." UGH!
by HappyGrrrl June 06, 2016
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