1.Definition: a region marking a boundary

Related Noun(s):brink, verge

Category: General

2.Definition: the entrance (the space in a wall) through which you enter or leave a room or building; the space that a door can close

Related Noun(s):door, doorway

Category: Objects

3.Definition: 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

Related Noun(s):doorsill, doorstep

Category: Objects

4.Definition: the smallest detectable sensation

Related Noun(s):limen

Category: General

5.Definition: the starting point for a new state or experience

"On the threshold of manhood"

Category: General