melatonin

noun

mel·​a·​to·​nin ˌme-lə-ˈtō-nən How to pronounce melatonin (audio)
: a vertebrate hormone that is derived from serotonin, is secreted by the pineal gland especially in response to darkness, and has been linked to the regulation of circadian rhythms

Examples of melatonin in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Is this what happens when Tamra finally douses herself in so much melatonin before filming that her fat tongue won’t move in her mouth? — Brian Moylan, Vulture, 28 Aug. 2026 Furthermore, the light emitted from screens appears to contribute to sleep disturbances by disrupting the release of melatonin, the hormone that helps regulate your sleep-wake cycle. — Erica D. Henn, The Conversation, 28 Aug. 2026 Packed with omega-3s, protein, fiber, and melatonin, these nutrient-dense nuts offer multiple health benefits. — Maggie O'Neill, Verywell Health, 28 Aug. 2026 Tryptophan is an amino acid that your body uses to produce serotonin and melatonin, both of which promote relaxation and better sleep. — Mura Dominko, Martha Stewart, 9 Aug. 2026 See All Example Sentences for melatonin

Word History

Etymology

mela-, extracted from Greek melan-, mélās "black, dark" + -tonin (in serotonin); so named because the hormone can lighten skin color in animals by reversing the effect of melanocyte-stimulating hormones — more at melano-

Note: The word was probably introduced in the first published description of the hormone's isolation: Aaron B. Lerner, et al., "Isolation of melatonin, the pineal gland factor that lightens melanocytes," Journal of the American Chemical Society, vol. 80, no. 10 (May 20, 1958), p. 2587.

First Known Use

1958, in the meaning defined above

Time Traveler
The first known use of melatonin was in 1958

Rhymes for melatonin

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Browse Nearby Words

melastome
melatonin
melatope
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Cite this Entry

“Melatonin.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/melatonin. Accessed 4 Sep. 2026.

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Kids Definition

melatonin

noun
mel·​a·​to·​nin ˌmel-ə-ˈtō-nən How to pronounce melatonin (audio)
: a hormone that is secreted by the pineal gland especially in response to darkness and has been linked to the regulation of bodily functions or activities (as sleep) that occur in approximately 24 hour cycles

Medical Definition

melatonin

noun
mel·​a·​to·​nin ˌmel-ə-ˈtō-nən How to pronounce melatonin (audio)
: a vertebrate hormone C13H16N2O2 that is derived from serotonin, is secreted by the pineal gland especially in response to darkness, and has been linked to the regulation of circadian rhythms

More from Merriam-Webster on melatonin

Britannica.com: Encyclopedia article about melatonin

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