let on

let on idiom
  1. Reveal one's true feelings or a fact, allow something to be known, as in Don't let on that you met her before. This usage is probably a shortening of let it on someone. [c. 1700]
  2. Pretend, as in He let on that he was very angry, but in fact he didn't care a bit. [First half of 1800s] Also see let in on.

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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