Pulley-block and Simple machine

Pulley-block noun - 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.

Simple machine and pulley-block are semantically related. In some cases you can use "Simple machine" instead a noun phrase "Pulley-block".

Simple machine noun - A device for overcoming resistance at one point by applying force at some other point.

Pulley-block and simple machine are semantically related. Sometimes you can replace phrase "Pulley-block" with "Simple machine", this phrases are similar.