melatonin

Etymology

The Shorter Oxford takes it as formed from English melano- + serotonin, from the first letters of the one and the end of the other.^[2] Merriam-Webster Unabridged, Webster's Third and Collins name melanocyte as the first part instead,^[3][4][5] and Merriam-Webster explains the name by the hormone's power to lighten melanocytes.^[3][4] The OED, Etymonline and the Oxford Dictionary of English go back directly to Ancient Greek μέλας (mélas, “black, dark”) for the first part, with the ending of the hormone's source;^[6][7][8] the American Heritage Dictionary and Dictionary.com have the Greek adjective with tone and the suffix -in.^[9][10] Stedman's medical dictionary derives it from melanophore and τόνος (tónos, “contraction”).^[11] Etymonline says the name was given either because sunlight checks its secretion or because it changes the skin colour of some reptiles and amphibians.^[7]

Earliest recorded meaning

A hormone made from serotonin in the pineal gland, which counteracts the hormone that darkens the skin: 1958, in a paper by A. B. Lerner and colleagues in the Journal of the American Chemical Society.^[6] Etymonline and Merriam-Webster also date the word to 1958.^[7][3]

Semantic evolution

The first descriptions stress its effect on skin colour: it lightens the pigment cells of amphibians and checks the formation of melanin.^[6][2][12] Later dictionaries add its role in the reproductive cycle,^[2][5] in sleep and ageing,^[13] and in the circadian rhythms, since it is secreted mainly in darkness.^[3][9] The American Heritage Dictionary now notes that it is also found in plants and fungi.^[9]

Timeline

• 1958 – a hormone of the pineal gland that lightens skin pigment cells.^[6][7][3]

Meanings

Noun

1. A hormone made from serotonin in the pineal gland, secreted mainly in darkness and involved in regulating sleep, circadian rhythms and reproductive cycles: Her doctor suggested a little melatonin for the jet lag.^[3][9][5]
2. The same substance in animals such as amphibians and reptiles, where it makes the skin change colour by lightening the melanocytes.^[9][4][2]

Related words

• serotonin
• melanin
• melanocyte
• melano-

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
3. ^ a b c d e f Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
4. ^ a b c Gove, Philip Babcock, ed. (1961), Webster's Third New International Dictionary of the English Language, Unabridged, Springfield, Mass.: G. & C. Merriam
5. ^ a b c Collins English Dictionary (2023), Glasgow: HarperCollins
6. ^ a b c d Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
7. ^ a b c d Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
8. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
9. ^ a b c d e The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
10. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
11. ^ Stedman's Medical Dictionary, Baltimore: Lippincott Williams & Wilkins
12. ^ Soanes, Catherine; Stevenson, Angus, eds. (2004), Concise Oxford English Dictionary, 11th ed., Oxford: Oxford University Press
13. ^ The American Heritage Dictionary of the English Language (2000), 4th ed., Boston: Houghton Mifflin