Escapement

Noun

1. The linkage in a (watch) that gives impulses to the timekeeping element and periodically releases the gear train to move forward, advancing the clock's hands.

   "The escapement is the reason why clocks tick."

2. A mechanism found in devices such as a typewriter or printer which controls lateral motion of the carriage.
3. An escape or a means of escape.
4. The number of fish that escape commercial fishing operations and travel upstream to spawn.