Definition of melatonin in English:



mass nounBiochemistry
  • 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.’


1950s from Greek melas ‘black’ + serotonin.