keep (something) under one's hat
idiom
: to keep (something) secret : to not tell anyone about (something)
I'll tell you what happened, but you have to keep it under your hat.
Cite this Entry
“Keep (something) under one's hat.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/keep%20%28something%29%20under%20one%27s%20hat. Accessed 27 Nov. 2025.
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