histamine

his·ta·mine

noun \ˈhis-tə-ˌmēn, -mən\

Definition of HISTAMINE

: a compound C₅H₉N₃ especially of mammalian tissues that causes dilatation of capillaries, contraction of smooth muscle, and stimulation of gastric acid secretion, that is released during allergic reactions, and that is formed by decarboxylation of histidine

—his·ta·min·ic \ˌhis-tə-ˈmin-ik\ adjective