/ Dictionary / Index C coplanar: Meaning and Definition of Find definitions for: co•pla•nar Pronunciation: (kō-plā'nur), [key] — adj. Math. being or operating in the same plane. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: coplanar (Thesaurus) copious Copland Related Content Daily Word Quiz: stringent Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language