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

For anyone burned by melatonin gummies, white noise machines and prescription sleep drugs, the timeline question is the one that matters most — how fast does Pulsetto actually work, and what does the company’s own data show? —Samantha Agate, Charlotte Observer, 4 June 2026

Blue-wavelength light tells the brain to suppress melatonin and stay sharp. —Allison Palmer updated June 4, Sacbee.com, 4 June 2026

Blue-light blocking glasses McCarty says that blue-light blocking glasses are based on a legitimate biological concept (that blue light affects circadian rhythms and melatonin production). —Sharon Brandwein, USA Today, 2 June 2026

And dosing can be particularly tricky because melatonin is a hormone that our bodies naturally produce, so individual needs vary significantly. —Mira Miller, Verywell Health, 2 June 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