escapement

noun4

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.

   • Importantly, there are also extensive practical difficulties associated with gathering and interpreting accurate escapement and run-size information and applying it to population management. — 1999