Plain English Meaning

The central spinning shaft inside the engine. The pistons push it round and round, and that spinning motion is what turns the propeller.

Full Definition

The main rotating shaft inside a piston engine that converts the up-and-down motion of the pistons into rotational motion. In an aircraft engine, the propeller is mounted directly to the crankshaft (or to a gearbox driven by it), so the crankshaft's rotation is what turns the propeller.

Context Anchor

Seen in piston-engine and constant-speed propeller discussions, especially when describing how engine power reaches the propeller.

Derivation

From 'crank,' meaning a bent arm or handle used to turn something, plus 'shaft.' The shaft has bends (cranks) along its length that the pistons push against, the same way you turn a to make a wheel .