Etymologically
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serum

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Pronunciation

  • UK: /ˈsɪəɹəm/, /ˈsiːɹəm/[1]
  • US: /ˈsɪɹəm/[1]

Etymology

It is borrowed from Latin serum (“whey, watery fluid”).[2][3][4][5][6] Etymonline, Barnhart and Klein connect the Latin noun with Ancient Greek ὀρός (orós, “whey”) and Sanskrit सरस् (sará-, “flowing”),[3][4][7][8] and Barnhart and Klein also with ὁρμή (hormḗ, “onset, impulse”),[4][7] the source of hormone;[7] all are referred to Proto-Indo-European *ser- (“to run, flow”).[3][4][7] Skeat gave the same comparison but noted a doubt.[9]

Earliest recorded meaning

The watery fluid of the animal body, normal or diseased, and especially the clear liquid that separates from blood when it clots: the OED's first quotation is from Richard Wiseman's Treatise of Wounds (1672).[2][10] Etymonline dates the word to the 1670s,[3] and Barnhart to 1672.[11][4] Merriam-Webster gives 1665 as the first known use,[8] and Dictionary.com 1655–65.[12]

Semantic evolution

Johnson (1755) defined serum first as the thin, watery part that separates from a liquid, as the whey from milk, and then as the part of the blood that separates from the clot.[13] At the end of the 19th century the word came to be used for blood serum taken from an immunized animal and used to treat or diagnose disease:[2][14] the OED's first example is from the British Medical Journal in 1895,[2] while Etymonline and Barnhart date this use to 1893.[3][4] From the mid-20th century serum is also used attributively for substances measured in the blood serum, as in serum cholesterol.[10] Both serums and the Latin plural sera are used.[14][8]

Timeline

  • 1665 – first known use, according to Merriam-Webster.[8]
  • 1672 – watery animal fluid; the fluid part of clotted blood.[2][4]
  • 1755 – Johnson defines it as the thin part of a liquid, as the whey of milk, and as the fluid part of the blood.[13]
  • 1893 – blood serum used in medical treatment.[3][4]
  • 1895 – serum used as a therapeutic or diagnostic agent.[2]
  • 1958 – attributive use for substances in the serum.[10]

Modern meaning

Noun

  1. The clear, pale yellow fluid that remains when blood clots; blood serum.
  2. Serum from an animal that has been immunized against a disease, containing antibodies and used to treat or prevent the disease: The doctors flew in a serum against the snakebite.
  3. Any watery fluid of the body, normal or diseased.
  4. A light, liquid cosmetic preparation applied to the skin or hair.

Word family

  • antiserum
  • serous
  • blood serum
  • immune serum
  • serum sickness
  • truth serum

References

  1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
  2. ^ a b c d e f Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
  3. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  4. ^ a b c d e f g h Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
  5. ^ Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
  6. ^ The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
  7. ^ a b c d Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
  8. ^ a b c d Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
  9. ^ Skeat, Walter W. (1911), A Concise Etymological Dictionary of the English Language, new ed., Oxford: Clarendon Press
  10. ^ a b c Kay, Christian; Roberts, Jane; Samuels, Michael; Wotherspoon, Irené, eds. (2009), Historical Thesaurus of the Oxford English Dictionary, Oxford: Oxford University Press; online edition (2024)
  11. ^ Barnhart, Robert K., ed. (1995), The Barnhart Concise Dictionary of Etymology, New York: HarperCollins
  12. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
  13. ^ a b Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
  14. ^ a b Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press