A Quick and Simple Dictionary

threshold

1. Noun.  The bottom-most part of a doorway that one crosses to enter; a sill.
2. Noun.  (context, by extension) An entrance.
3. Noun.  The start of the landing area of a runway.
4. Noun.  (engineering) The quantitative point at which an action is triggered, especially a lower limit.
5. Noun.  The wage or salary at which income tax becomes due.
6. Noun.  The outset of an action or project.
7. Noun.  The point where one mentally or physically is vulnerable in response to provocation or to particular things in general. As in emotions, stress, or pain.
8. Noun.  The point of beginning or entry.