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

Oura Ring emphasizes morning sunlight in its education content, noting that first-thing sunlight suppresses melatonin and increases cortisol, and positions itself as a tool to track sleep and validate sunmaxxing habits. — Hanna Wickes, Charlotte Observer, 21 July 2026

High ambient temperatures disrupt melatonin production because the body must cool down to initiate deep REM sleep. — Nicole F. Roberts, Forbes.com, 20 July 2026

Tart cherries naturally contain melatonin and antioxidant compounds called anthocyanins, which is why dietitians sometimes recommend a small glass in the evening as a gentler alternative to pills. — Lauren Jarvis-Gibson july 18, Fort Worth Star-Telegram, 18 July 2026

And the dog that paces through every thunderstorm, or chews a cushion to pieces the moment the house goes quiet, has a calming soft chew made with chamomile, melatonin, and L-theanine. — Daniel Fusch, USA Today, 17 July 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