Definition of melatonin in English:


Syllabification: mel·a·to·nin
Pronunciation: /ˌmeləˈtōnin


  • A hormone secreted by the pineal gland that inhibits melanin formation and is thought to be concerned with regulating the reproductive cycle.
    More example sentences
    • 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.


1950s: from Greek melas 'black' + (sero)tonin.

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a slit made by cutting with a saw