pulley

n. wheel with a grooved rim around which a rope or cord is wrapped (when one end of the rope is pulled downward, the wheel spins and raises the opposite end)

A pulley (also called a sheave or block) is a wheel with a groove between two flanges around its circumference. The groove normally locates a rope, cable or  belt. Pulleys are used to change the direction of an applied force, transmit rotational motion, or realize a mechanical advantage in either a linear or rotational system of motion.
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Noun
1. a simple machine consisting of a wheel with a groove in which a rope can run to change the direction or point of application of a force applied to the rope
(synonym) pulley-block, block
(hypernym) machine, simple machine
(hyponym) bollock, bullock block
(part-holonym) block and tackle

(v. t.)
A wheel with a broad rim, or grooved rim, for transmitting power from, or imparting power to, the different parts of machinery, or for changing the direction of motion, by means of a belt, cord, rope, or chain.
  

(b. t.)
To raise or lift by means of a pulley.
  

A Pulley that is normally attached to the wellhead at a convenient place for the wireline to pass through as it comes from the stuffing box sheave before being spooled onto the wireline reel. The hay pulley prevents any lateral force from being exerted on the lubricator and the Wellhead