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
A hormone, C13H16N2O2, derived from serotonin and produced by the pineal gland. It stimulates color change in the epidermis of amphibians and reptiles and plays a role in the function of circadian rhythms and estrous cycles in mammals.
Origin of melatoninGreek melās, black + ton(e) + –in.
(usually uncountable, plural melatonins)