1. A piece of wood or stone placed beneath a door; a doorsill.
2. An entrance or a doorway.
3. The place or point of beginning; the outset.
4. The point that must be exceeded to begin producing a given effect or result or to elicit a response: a low threshold of pain.

[Middle English thresshold, from Old English therscold, threscold.]

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.