1. A rounded blade that revolves in a circle: A propeller can be used to move a vehicle by pressing or pushing against air, like in a plane, or by spinning against water, like in a speed boat!
2. Something or someone that drives or forces something onward: As a propeller for the continuation of the fascinating story, the two protagonists, Jim and Carolyn, who didn't know they were actually siblings, fell in love with each other.

A propeller whose pitch is regulated by an electric motor.

A part of a machine in which the angle of the blades of a power-driven shaft can be adjusted to suit different conditions while maintaining the same engine speed.