/ Dictionary / Index C cosponsor: Meaning and Definition of Find definitions for: co•spon•sor Pronunciation: (kō-spon'sur), [key] — n. a joint sponsor, as of a legislative bill. —v.t. to act as cosponsor for. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: cosponsor (Thesaurus) cosmotron coss Related Content Daily Word Quiz: blithesome Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language