Main Entry: mel·a·to·nin

Pronunciation: \ˌme-lə-ˈtō-nən\

Function: noun

Etymology: Greek melas black + -tonin (as in serotonin)

Date: 1958

: 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