Ironically or as a joke, as in Was he speaking with tongue in cheek when he said Sally should run for president? This term probably alludes to the facial expression produced by poking one's tongue in one's cheek, perhaps to suppress a smile. [First half of 1800s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.