melatonin

noun

mel·​a·​to·​nin ˌme-lə-ˈtō-nən 

: 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

Deepkold offers Focus and Energy pouches with 50 mg caffeine and 50 mg L-theanine, a caffeine-free Shroom Frost built around lion’s mane, cordyceps, reishi and B12, and Deep Calm for sleep with melatonin, L-theanine and magnesium glycinate. — Hanna Wickes, Kansas City Star, 20 Oct. 2026

Brands are now repurposing the same under-the-lip delivery system for caffeine, cannabis, vitamins and melatonin, with nootropic pouches sitting at the newest edge of that shift. — Hanna Wickes, Charlotte Observer, 20 Oct. 2026

Walnuts Among the few foods that naturally contain melatonin, walnuts also carry omega-3s that support the brain’s serotonin pathway. — Patsy Anthony, Vogue, 19 Oct. 2026

Some nuts also contain melatonin, which helps regulate your sleep-wake cycle. — Sarah Jividen, Verywell Health, 8 Oct. 2026

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

Rhymes for melatonin

• calcitonin
• digitonin
• serotonin
• kronen
• onan
• phonon
• ronin
• santonin

Kids Definition

melatonin

noun

mel·​a·​to·​nin ˌmel-ə-ˈtō-nən 

: 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 

: 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