threshold

noun8

1. •
   The lowermost part of a doorway that one crosses to enter; a sill.
2. •
   The quantitative point at which an action is triggered, especially a lower limit.
3. •
   The wage or salary at which income tax becomes due.
4. •
   The point where one is mentally or physically vulnerable in response to a provocation or to other nuisances.
5. •
   An entrance; the door or gate of a house.

   • Shy. You that did voide your rume vpon my beard, / And foote me as you spurne a stranger curre / Ouer your threshold, […] — 1596
6. •
   (figurative) The outset of something; the point of entry, or the beginning of an action.

   • The first half of this century has been referred to as the golden age of medicine. To me it seems more probable that we are on the threshold of a much greater age. — 1951
7. •
   Any end or boundary.
8. •
   The start of the landing area of a runway.