threshold in WordNet English dictionary

1. a region marking a boundary
   brink  threshold  verge 
   
2. the entrance (the space in a wall) through which you enter or leave a room or building; the space that a door can close
   "he stuck his head in the doorway"
   doorway  door  room access  threshold 
   
3. the sill of a door; a horizontal piece of wood or stone that forms the bottom of a doorway and offers support when passing through a doorway
   doorsill  doorstep  threshold 
   
4. the smallest detectable sensation
   threshold  limen 
   
5. the starting point for a new state or experience
   "on the threshold of manhood"
   threshold