escapement

noun

1. Rare the action of escaping or a means of escape
2. the part in a mechanical clock or watch that controls the speed and regularity of the balance wheel or pendulum, and thereby of the entire mechanism, by the movement of a notched wheel (), one tooth of which is permitted to escape from the detaining catch at a time
3. a ratchet mechanism, esp. one in typewriters that regulates the horizontal movement of the carriage