threshold

Noun

• a region marking a boundary

• 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

• 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
    

• the smallest detectable sensation

• the starting point for a new state or experience
  • on the threshold of manhood
    

Related words

• Synonyms: 
  brink , verge , doorsill , doorstep , doorway , door , room access , limen