/ Dictionary / Index O onside: Meaning and Definition of Find definitions for: on•side Pronunciation: (on'sīd', ôn'-), [key] — adj., adv. Sports. not offside; being within the prescribed line or area at the beginning of or during play or a play. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: onside (Thesaurus) onshore onside kick Related Content Daily Word Quiz: cautious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language