/ Dictionary / Index C Cosa Nostra: Meaning and Definition of Find definitions for: Co•sa Nos•tra Pronunciation: (kō'zu nōs'tru), [key] a secret association engaged in organized crime in the U.S., modeled after and affiliated with the Mafia. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. cos Cosby 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