a hormone, CHNO, produced by the pineal body, that lightens skin pigmentation, inhibits estrus, etc.: its secretion is inhibited by sunlight
Origin of melatoninmela(no)- + (sero)tonin
An animal hormone, C13H16N2O2, derived from serotonin and produced by the pineal gland. It stimulates color change in the skin of amphibians and reptiles and plays a role in regulating circadian rhythms and reproductive cycles in mammals. It is also found in plants and fungi.
Origin of melatoninGreek melās black ton(e) -in
(usually uncountable, plural melatonins)