/ Dictionary / Index O OI: Meaning and Definition of Find definitions for: OI Pronunciation: [key] opportunistic infection. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Ohrmazd OIC Related Content Daily Word Quiz: perspicacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language