threshold -- (the starting point for a new state or experience; "on the threshold of manhood")
threshold, limen -- (the smallest detectable sensation)
doorway, door, room access, threshold -- (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")
doorsill, doorstep, threshold -- (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)
brink, threshold, verge -- (a region marking a boundary)
(Sound)
