/ Dictionary / Index C costate: Meaning and Definition of Find definitions for: cos•tate Pronunciation: (kos'tut, kô'stāt), [key] — adj. having ribs. (of mosses) having a midrib or costa. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: costate (Thesaurus) Costa Rica cost-benefit Related Content Daily Word Quiz: gregarious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language