From The Collaborative International Dictionary of English v.0.48 [gcide]:
3. The contrivance in a timepiece which connects the train of wheel work with the pendulum or balance, giving to the latter the impulse by which it is kept in vibration; -- so called because it allows a tooth to escape from a pallet at each vibration.
Note: Escapements are of several kinds, as the vertical, or verge, or crown, escapement, formerly used in watches, in which two pallets on the balance arbor engage with a crown wheel; the anchor escapement, in which an anchor-shaped piece carries the pallets; -- used in common clocks (both are called recoil escapements, from the recoil of the escape wheel at each vibration); the cylinder escapement, having an open-sided hollow cylinder on the balance arbor to control the escape wheel; the duplex escapement, having two sets of teeth on the wheel; the lever escapement, which is a kind of detached escapement, because the pallets are on a lever so arranged that the balance which vibrates it is detached during the greater part of its vibration and thus swings more freely; the detent escapement, used in chronometers; the remontoir escapement, in which the escape wheel is driven by an independent spring or weight wound up at intervals by the clock train, -- sometimes used in astronomical clocks. When the shape of an escape-wheel tooth is such that it falls dead on the pallet without recoil, it forms a deadbeat escapement.
From WordNet (r) 3.0 (2006) [wn]:
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