means A very brief, indefinite period of time — or a particular point in time, sometimes one of special importance.

from From Latin 'momentum,' meaning a movement, motion, or — crucially — the tiny tipping motion of a balance scale, the smallest weight that makes the pans shift. 'Momentum' itself contracted from 'movimentum,' from 'movere,' to move. So a moment was originally the instant the scale tipped: time measured as the smallest noticeable shift. The same word later branched off into 'momentum' in physics, where it kept the sense of motion, while 'moment' kept the sense of the flicker of time in which that motion happens.