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in the act

in the act idiom

In the process of doing something. For example, The police caught the robber in the act, or I was in the act of closing the window. [Second half of 1600s]
Performing sexual intercourse, as in Her father caught them in the act. [Late 1500s]

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.