/ Dictionary / Index P periodic motion: Meaning and Definition of Find definitions for: pe'ri•od'ic mo'tion Pronunciation: (pēr'ē-od'ik, pēr"-), [key] — Physics. Physics. any motion that recurs in identical forms at equal intervals of time. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. periodic law periodic sentence Related Content Daily Word Quiz: philately Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language