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

Key Takeaways While more research is needed, current studies suggest that kiwi may support better sleep due to its serotonin, melatonin, and antioxidant properties. —Kathleen Ferraro, Verywell Health, 4 Sep. 2025

If your doctor gives you the go-ahead to use melatonin, follow their advice. —Julia Forbes, Wired News, 29 Aug. 2025

This inhibits the promotion of natural melatonin and shoots adrenaline to create an alertness effect creating a tired but wired effect, says Marchetti. —Sherri Gordon, Parents, 26 Aug. 2025

Magnesium supplements, which help support melatonin production, have skyrocketed in popularity in recent years, according to reports, surpassing even fish oil and probiotics. —Deirdre Bardolf, FOXNews.com, 23 Aug. 2025

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