n. (Chem.) An organic base, especially one of a class of nitrogen-containing substances occurring ready formed in the tissues of plants and the bodies of animals. [ 1913 Webster ]

☞ Alkaloids all contain nitrogen, carbon, and hydrogen, and many of them also contain oxygen. They include many of the active principles in plants; thus, morphine and narcotine are alkaloids found in opium. [ 1913 Webster ]

{ } a. [ Alkali + -oid: cf. F. alcaloïde. ] 1. Pertaining to, resembling, or containing, alkali. [ 1913 Webster ]

2. of or pertaining to alkaloids. [ WordNet 1.5 ]