Definition of melatonin in English:

melatonin

Pronunciation /ˌmeləˈtōnən/ /ˌmɛləˈtoʊnən/

noun

Biochemistry
  • A hormone secreted by the pineal gland which inhibits melanin formation and is thought to be concerned with regulating the reproductive cycle.

    ‘The pineal gland hormone, melatonin, is one of the endproducts regulated by the circadian system.’
    • ‘Delaying sleep on weekends delays the nightly secretion of melatonin, the sleep hormone.’
    • ‘Research has found the pineal hormone melatonin is low in migraine patients.’
    • ‘Cherries are also a great source of melatonin, a hormone that your body uses to regulate its sleep patterns.’
    • ‘Bright light in the morning affects your levels of the hormone melatonin.’

Origin

1950s from Greek melas ‘black’+ serotonin.