means The tendency of any object to keep doing what it's already doing — staying still or moving steadily — unless some force intervenes.

from From Latin 'iners,' meaning idle, unskilled, or sluggish (literally 'without art' — 'in-' not + 'ars' skill). The German astronomer Kepler borrowed it in the early 1600s, and Newton cemented it as a physics term for matter's resistance to changes in its motion. So a word that once meant 'lazy and useless' became the universe's official excuse for never lifting a finger.