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

With a blend of melatonin, peptides, and antioxidants, the Spanish formula has a stamp of approval from celebrity esthetician Taylor Worden. —Jenny Berg, Vogue, 25 Mar. 2025

And for the love of melatonin, keep your eyes away from your blue-light-emitting devices before bed. —Erica Sloan, SELF, 24 Mar. 2025

Extended-release melatonin may raise your body’s melatonin levels within 15 minutes, keeping levels up for six hours. —Elizabeth Barnes, Verywell Health, 19 Mar. 2025

Get morning sunlight exposure, which may improve your body's evening melatonin production14 Maintain a healthy diet A Quick Review Magnesium and melatonin are two supplements people commonly use to improve their sleep quality. —Kirstyn Hill, Pharmd, Mph, Health, 10 Mar. 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