melatonin
mel·a·to·nin
noun \ˌme-lə-ˈtō-nən\Definition of MELATONIN
: a vertebrate hormone that is derived from serotonin, is secreted by the pineal gland especially in response to darkness, and has been linked to the regulation of circadian rhythms
See Origin of MELATONIN
Greek melas black + -tonin (as in serotonin)
First Known Use: 1958
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