Idioms and Phrases with won't wash
won't wash
Will not stand up to examination, is unconvincing, will not work, as in That excuse about your sick aunt just won't wash. This expression originally alluded to a fabric that would not stand up to washing but by the late 1800s was used figuratively for other kinds of failure.
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The American Heritage® Idioms Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.