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

Both Peruvemba and Newgent point to magnesium-rich foods and melatonin-containing foods as key players in nighttime nutrition. —Lynn Andriani, Martha Stewart, 19 Apr. 2026

Even low-level ambient light during sleep continues suppressing melatonin through the night. —Allison Palmer, Fort Worth Star-Telegram, 17 Apr. 2026

The International Pediatric Sleep Association’s 2025 expert consensus guidelines recommend treating melatonin as a medication rather than a casual supplement in children, with use guided by a clinician. —Allison Palmer, Sacbee.com, 16 Apr. 2026

Dim the Lights Earlier in the Evening The lighting level in your home in the hours before bed has a direct effect on melatonin production, which weakens with age regardless. —Allison Palmer, Kansas City Star, 16 Apr. 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