/ Dictionary / Index C Costello: Meaning and Definition of Find definitions for: Cos•tel•lo Pronunciation: (kos'tl-ō", ko-stel'ō), [key] — n. 1891–1976, Irish political leader: prime minister of the Republic of Ireland 1948–51, 1954–57. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. cost-efficient coster 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