APAD: A skeleton in the closet
Meaning:
Despite appearances to the contrary, there is a well-hidden secret that could be
damaging or embarrassing.
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I first met a similar expression in the dear old New Concept English 3 where
someone has a real skeleton in his cupboard and scared the hell out of his friend.
Then it appeared in the British comedy "Four Weddings and a Funeral" where
Charles (played by Hugh Grant) was delivering his best-man speech at a wedding:
"Today we're talking about Angus. There were no skeletons in HIS cupboard. Or so
I thought!"
So it seems the Brits prefer 'cupboard' to 'closet.'