/ Dictionary / Index C C.I.O.: Meaning and Definition of Find definitions for: C.I.O. Pronunciation: [key] chief investment officer. See Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: cio (Thesaurus) Cinque Ports cion Related Content Daily Word Quiz: reclusive Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language