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

Mini bars burst with silk eye covers, collagen masks, melatonin sprays and ear plugs, suggesting the bacchanalia Estelle encourages. —Condé Nast, Condé Nast Traveler, 18 May 2026

No dosage of melatonin, Ambien, or trazodone, and no quantity of alcohol. —Weike Wang, New Yorker, 17 May 2026

Night shift workers produce 34-54% less melatonin over a 24-hour period than day workers, with the steepest suppression among people whose natural preference is daytime activity. —Allison Palmer, Fort Worth Star-Telegram, 16 May 2026

Bright light in the 2,500-10,000 lux range during the first six hours of a shift suppresses melatonin and sharpens alertness. —Allison Palmer, Sacbee.com, 15 May 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