means To move or spin rapidly with a continuous low buzzing or humming sound, or the sound itself.

from An imitative word — coined to mimic the very noise it names, the way 'buzz' and 'hum' are. It surfaced in late Middle English, possibly nudged along by Scandinavian relatives like the Danish 'hvirre' (to twirl) and Norwegian 'kvirra' (to whirl), all built from the same restless idea of fast, circling motion. So when something whirs, the word is literally doing an impression of it.