expansion bolt definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a bolt with an attachment that expands as the bolt is screwed in so as to anchor it in place, used in holes drilled in stone, concrete, etc.
expansion bolt definition by American Heritage Dictionary
A bolt having an attachment that expands as the bolt is driven into a surface.