a wheel, with a grooved rim for carrying a line, that turns in a frame or block and serves to change the direction of or to transmit force, as when one end of the line is pulled to raise a weight at the other end

one of the simple machines.

a combination of such wheels in a block, or of such wheels or blocks in a tackle, to increase the force applied.

a wheel driven by or driving a belt or the like, used to deliver force to a machine, another belt, etc., at a certain speed and torque.

noun

block , machine , ring , sheave , wheel