/ Dictionary / Index Q quantum mechanics: Meaning and Definition of Find definitions for: quan'tum mechan'ics Pronunciation: [key] — Physics. Physics. a theory of the mechanics of atoms, molecules, and other physical systems that are subject to the uncertainty principle. Abbr.: QM Cf. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. quantum jump quantum number Related Content Daily Word Quiz: lunar Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language