/ Dictionary / Index O on-peak: Meaning and Definition of Find definitions for: on-peak Pronunciation: (on'pēk', ôn'-), [key] — adj. peak (def. 17). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Onondaga ONR Related Content Daily Word Quiz: blithesome Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language