keep something under your hat

keep something under your hat

INFORMAL
If you keep something under your hat, you do not tell anyone else about it. Very few people know, so keep it under your hat. Look, if I tell you something will you promise to keep it under your hat? Note: This was a slogan used to promote security in Britain during the Second World War.
See also: hat, keep, something

keep something under your hat

keep something a secret.
See also: hat, keep, something

ˌkeep something under your ˈhat

(informal) keep something secret: I’m going to apply for another job, but keep it under your hat for a while, will you? OPPOSITE: let the cat out of the bag
See also: hat, keep, something
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