escapement

Short definition from Wiktionary

Noun

1. 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.
2. 2
   A mechanism found in devices such as a typewriter or printer which controls lateral motion of the carriage.
3. 3
   An escape or a means of escape.
4. 4
   The number of fish that escape commercial fishing operations and travel upstream to spawn.