Noun
1. the starting point for a new state or experience;
"on the threshold of manhood"2. the smallest detectable sensation
3. 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"4. the sill of a door; a horizontal piece of wood or stone that forms the bottom of a doorway and offer support when passing through a doorway
5. a region marking a boundary