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.

In naval architecture, an arrangement of two propellers on a single shaft.

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.