Threshold

threshold

1. 1:  the plank, stone, or piece of timber that lies under a door :  sill
2. 2a :  gate, doorb (1) :  end, boundary; specifically :  the end of a runway (2) :  the place or point of entering or beginning :  outset threshold

 of a new age>

3a :  the point at which a physiological or psychological effect begins to be produced threshold

 for pain>b :  a level, point, or value above which something is true or will take place and below which it is not or will not