Meanings
nounmelatonin (usually uncountable, plural melatonins)
plural melatonins
- uncountableusuallyA 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 3101 more example
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 - uncountableusuallyAny material similar in its chemistry and effect to the natural hormone.
Origin
- Ancient Greekμέλας“black, dark”
- Englishmelatonin
From mela- + tone + -in, ultimately from Ancient Greek μέλας (mélas, “black, dark”).
More words from Ancient Greek
Full word history & related roots →Translations
Bulgarian мелатоним
- мелатоним (melatonim)hormone
Catalan melatonina
- melatoninahormone
Chinese Mandarin 褪黑素
- 褪黑素 (tuìhēisù)hormone
Danish melatonin
- melatoninhormone
Dutch melatonine
- melatoninehormone
Finnish melatoniini
- melatoniinihormone
French mélatonine
- mélatoninehormone
German Melatonin
- Melatoninhormone
Greek μελατονίνη
- μελατονίνη (melatoníni)hormone
Hungarian melatonin
- melatoninhormone
Irish meileatoinin
- meileatoininhormone
Italian melatonina
- melatoninahormone
Japanese メラトニン
- メラトニン (meratonin)hormone
Korean 멜라토닌
- 멜라토닌 (mellatonin)hormone
Latvian melatonīns
- melatonīnshormone
Persian ملاتونین
- ملاتونینhormone
Polish melatonina
- melatoninahormone
Russian мелатони́н
- мелатони́н (melatonín)hormone
Spanish melatonina
- melatoninahormone
Swedish melatonin
- melatoninhormone
Tamil மெலட்டோனின்
- மெலட்டோனின் (melaṭṭōṉiṉ)hormone
Thai เมลาโทนิน
- เมลาโทนินhormone
Turkish melatonin
- melatoninhormone
Ukrainian мелатоні́н
- мелатоні́н (melatonín)hormone
Welsh melatonin
- melatoninhormone
Rhymes & wordplay
Anagrams
Cite this entry
APA
melatonin. (n.d.). In WatkinsX Dictionary. Retrieved November 2, 2026, from https://dictionary.watkinsx.com/word/melatonin
MLA
“melatonin.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/melatonin. Accessed November 2, 2026.
Chicago
WatkinsX Dictionary, s.v. “melatonin,” accessed November 2, 2026, https://dictionary.watkinsx.com/word/melatonin.
Source: melatonin on Wiktionary, CC BY-SA 4.0.