{ Al"ka*loid (ăl"k&adot;*loid), Al`ka*loid"al (ăl`k&adot;*loid"al), } a. [Alkali + -oid: cf. F. alcaloïde.] Pertaining to, resembling, or containing, alkali.

Al"ka*loid (ăl"k&adot;*loid), n. (Chem.) An organic base, especially one of a class of substances occurring ready formed in the tissues of plants and the bodies of animals.

&fist; 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.

• (Chemistry) Any of many organic heterocyclic bases, that occur in nature and often have medicinal properties.