/ Dictionary / Index O ONI: Meaning and Definition of Find definitions for: ONI Pronunciation: [key] Office of Naval Intelligence. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: oni (Thesaurus) ongoing -onic Related Content Daily Word Quiz: rustic Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language