The stone, plank, or piece of timber under a door; a doorsill.

门槛。

An entrance; a door.

入口；门口。

The place or occasion of entering upon or beginning something.

(常用单数)开始；发轫。

Degree of intensity at which a stimulus becomes perceptible.

【心理】阈限；临界(强度，对刺激的敏感度)。