Await a seemingly inevitable event, as in Now that she has a good enough job to leave her husband, we're just waiting for the other shoe to drop. This expression alludes to a person awakened by a neighbor who loudly dropped one shoe on the floor and is waiting for the second shoe to be dropped. [Early 1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.