/ Dictionary / Index C chorion: Meaning and Definition of Find definitions for: cho•ri•on Pronunciation: (kôr'ē-on", kōr'-), [key] — n. the outermost of the extraembryonic membranes of land vertebrates, contributing to the formation of the placenta in the placental mammals. the membrane around the eggs of certain insects, secreted by cells of the ovary. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: chorion (Thesaurus) chorioma chorionic gonadotropin Related Content Daily Word Quiz: morose Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language