/ Dictionary / Index C cysteine: Meaning and Definition of Find definitions for: cys•te•ine Pronunciation: (sis'tē-ēn", -in), [key] — n. Biochem. a crystalline amino acid, CHONS, a component of nearly all proteins, obtained by the reduction of cystine. Abbr.: Cys; Symbol: C Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: cysteine (Thesaurus) cystectomy cysti- Related Content Daily Word Quiz: foliage Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language