melatonin
nounUK /ˌmɛləˈtəʊnɪn/ · CA, US /ˌmɛləˈtoʊnɪn/
Etymology From mela- + tone + -in, ultimately from Ancient Greek μέλας (mélas, “black, dark”).
1
Usually A hormone, related to serotonin, that is secreted by the pineal gland, and stimulates colour change in the skin of reptiles, and is involved in the sleep and wake and reproductive cycles in mammals.
- How exactly melatonin relates to sleep is still not understood.2019, Bill Bryson, The Body: A Guide for Occupants, Black Swan (2020), page 310:
- Melatonin production can be delayed or arrested by even brief flashes of bright light entering the eye, research has shown.2025 December 9, Veronique Greenwood, “Your Bedroom Probably Isn't Dark Enough”, in TIME:
2
Usually Any material similar in its chemistry and effect to the natural hormone.
- Derived terms
- melatonergic