blow one's 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. © 2015 Farlex, Inc, all rights reserved.

blow one's cover

Inadvertently give away one's secret identity, as in Mary came to the annual meeting pretending to be a shareholder and hoped no one would blow her cover . This expression uses blow in the sense of "expose or betray," a usage dating from Shakespeare's day.
See also: blow, cover
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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