/ Dictionary / Index C CYO: Meaning and Definition of Find definitions for: CYO Pronunciation: [key] Catholic Youth Organization. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Cynwulf cyperaceous Related Content Daily Word Quiz: clairvoyant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language