blow cover

blow (one's) cover

To expose one's true identity or motives after they had been intentionally concealed (i.e. after one had been "undercover"). The spy fled when he realized that someone had blown his cover. I totally blew my cover when I stupidly wore my school jacket to steal the other team's mascot.
See also: blow, cover
Farlex Dictionary of Idioms. © 2022 Farlex, Inc, all rights reserved.

blow someone's cover

Sl. to reveal someone's true identity; to ruin someone's scheme for concealment. The dog recognized me and blew my cover. I didn't mean to blow your cover by calling out to you.
See also: blow, cover
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
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References in periodicals archive ?
No one has ever been convicted - despite a widely held belief that those who witnessed the blow covered each others' backs.
| WIDESPREAD DAMAGE: HEAVY BLOW covers (JH180613Hlinthwaite) one of the manhole covers (JH180613Hlinthwaite) UNDERGROUND explosions blowing heavy manhole covers into the air made the news this week - but not for the first time.
Most of the objects were preserved after a "catastrophic" sand blow covered them up between the 1770s and the late 1840s.