Codeine \Co*de"ine\, n. [Gr. ? poppy head: cf. F. cod?ine.] (Chem.) One of the opium alkaloids; a white crystalline substance, {C18H21NO3}, similar to and regarded as a derivative of morphine, but much feebler in its action; -- called also {codeia}.
codeine n : derivative of opium; used as an antitussive (to relieve coughing) and an analgesic (to relive pain)