the.com/camshaft

means A rotating rod studded with egg-shaped lobes (cams) that push open an engine's valves at precisely timed moments, then let them snap shut.

from A straightforward compound: 'cam' — borrowed in the 1700s from Dutch/Scandinavian 'kam,' meaning comb, describing a toothed or notched wheel used in machinery — plus 'shaft,' the old English word for a long rod or pole. The cam's odd lobed shape literally resembled comb teeth as it turned, converting round-and-round rotation into precisely timed up-and-down motion — which is exactly what it still does, pushing valves open on cue.