Also, the bottom falls out. A collapse occurs, as in The bottom dropped out of the steel market, or When they lost the game, the bottom fell out of their hopes to make the playoffs. This term alludes to collapsing deeper than the very lowest point, or bottom. [First half of 1600s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.