noun pl. pulleys -·leys

1. a small fixed wheel, sometimes turning in a block, with a grooved rim in which a rope or chain runs, as to raise a weight attached at one end by pulling on the other end: it changes the direction of effort but provides no mechanical advantage
2. a combination of such wheels, used to increase the mechanical advantage
3. a wheel that turns or is turned by a belt, rope, chain, etc., so as to transmit power

Etymology: ME poley < OFr polie < ML poleia < poledia < MGr *polidion, dim. of polos, pivot, windlass, axis: see wheel