blow one's cover

blow one's cover idiom
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.

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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