melatonin

From mela- +‎ tone +‎ -in, ultimately from Ancient Greek μέλας (mélas, “black, dark”).

• (Received Pronunciation) IPA^(key): /ˌmɛləˈtəʊnɪn/
• (General American, Canada) IPA^(key): /ˌmɛləˈtoʊnɪn/

  • Audio (North Carolina):

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• (General Australian) IPA^(key): /ˌmeləˈtəʉnɪn/
• (New Zealand) IPA^(key): /ˌmeləˈtɐʉnən/

melatonin (usually uncountable, plural melatonins)

1. 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.
   • 2019, Bill Bryson, The Body: A Guide for Occupants, Black Swan (2020), page 310:

     How exactly melatonin relates to sleep is still not understood.

   • 2025 December 9, Veronique Greenwood, “Your Bedroom Probably Isn't Dark Enough”, in TIME‎^[1]:

     Melatonin production can be delayed or arrested by even brief flashes of bright light entering the eye, research has shown.

2. Any material similar in its chemistry and effect to the natural hormone.

Borrowed from English melatonin.

melatonin c (singular definite melatoninen, not used in plural form)

1. melatonin