1a mechanism in a clock or watch that alternately checks and releases the train by a fixed amount and transmits a periodic impulse from the spring or weight to the balance wheel or pendulum:a lever escapement
2a mechanism in a typewriter that shifts the carriage a small fixed amount to the left after a key is pressed and released.
3the part of the mechanism in a piano that enables the hammer to fall back as soon as it has struck the string.
late 18th century: from French échappement, from échapper 'to escape'
escapement in other Oxford dictionaries
Definition of escapement in the US English dictionary