/ Dictionary / Index C Costain: Meaning and Definition of Find definitions for: Cos•tain Pronunciation: (kos'tān), [key] — n. 1885–1965, U.S. novelist, historian, and editor, born in Canada. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Costa del Sol costal Related Content Daily Word Quiz: penchant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language