1. 1. A collapse, as of a tunnel or structure.
   2. A place where a cave-in has occurred.
2. An act or instance of ceasing opposition or resistance: The vote was seen as a cave-in to the demands of the administration.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.