serum

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

Related words

• sero-
• whey
• hormone
• plasma
• lymph

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