noun.
An alkaloid narcotic, C18H21NO3, derived from opium or morphine and used as a cough suppressant, analgesic, and hypnotic.
The Century Dictionary and Cyclopedia
noun.
A white crystalline alkaloid (C18H21NO3 + H2O) contained in opium to the extent of 0.1 to 0.8 per cent. It is used as a hypnotic and to quiet coughs and pain. Also written codein, codeina, and codeia.
the GNU version of the Collaborative International Dictionary of English
noun.
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.