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

Świątek ended up with a one-month ban despite taking a melatonin pill recommended by her doctor as safe. —Charlie Eccleshare, New York Times, 14 May 2025

Try reaching for a handful of nuts (which contain melatonin), a glass of milk (which may support better sleep), or some cherry juice (which helps regulate sleep hormones). —Meg Walters, Glamour, 14 May 2025

Taking Melatonin There is good evidence in some cases for using melatonin to promote sleep, said Dr. Vendrame. —Sherri Gordon, Health, 12 May 2025

The study also revealed that 42 percent of children later diagnosed with autism had used melatonin within the past month, a common remedy for sleep difficulties, suggesting a possible attempt by parents to manage early sleep challenges. —Daniella Gray, MSNBC Newsweek, 11 May 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