se·​rum | \ ˈsir-əm How to pronounce serum (audio) \
plural sera\ ˈsir-​ə How to pronounce serum (audio) \ or serums

Definition of serum

 (Entry 1 of 2)

1 : the watery, clear portion of an animal fluid:
a : the clear, yellowish fluid that remains from blood plasma after clotting factors (such as fibrinogen and prothrombin) have been removed by clot formation : blood serum — compare antiserum, convalescent serum
b : a normal or pathological serous fluid (as in a blister)
c : whey
2 : a usually lightweight cosmetic preparation especially for use on the face specifically : a typically water-based, often concentrated preparation that lacks lubricating and thickening agents an antiaging facial serum
3 : the watery part of a plant fluid Latex. This, the natural product of the rubber tree, is a suspension of rubber droplets in a watery serum concentrated and stabilized in such a way that the dry rubber content is between 60 and 70 per cent.— C. A. O'Flaherty — see also truth serum



Definition of serum (Entry 2 of 2)

: occurring or found in the blood serum serum cholesterol serum antibodies

Examples of serum in a Sentence

Noun The patient was administered serum.
Recent Examples on the Web: Noun However, the hydration this plumper provided was a perk, as the serum left her lips feeling moisturized even after wiping it off. Alyssa Brascia, Peoplemag, 10 Aug. 2022 The 17 gifts below are catered to those of us—or that one friend or relative—who would rather throw cash at bottles of serum than bottles of champagne. Jenna Rosenstein, Harper's BAZAAR, 29 July 2022 The lightweight serum helps boost the skin’s natural glow. Chris Hachey, BGR, 28 July 2022 An instant bestseller, Verdejo landed the serum at, and in Urban Outfitters. Janel Martinez,, 27 July 2022 And Seppala promptly departed for Nenana, where a shipment of serum awaited. David Reamer, Anchorage Daily News, 24 July 2022 Unlike other nail hardeners that are more like lacquers, this Good Housekeeping Beauty Award winner has a serum-like texture that absorbs quickly into nails without leaving any film or coating on nails. Danusia Wnek, Good Housekeeping, 29 June 2022 With that comes low-maintenance, dewy serum-like foundations and tints. Sarah Madaus, SELF, 31 May 2022 This serum-like primer also uses one of my favorite skincare ingredients, niacinamide, which protects the skin from environmental aggressors while also treating breakouts. ELLE, 24 May 2022 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'serum.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of serum


1651, in the meaning defined at sense 1


1876, in the meaning defined above

History and Etymology for serum


borrowed from Latin, "whey, wheylike fluid," of uncertain origin

Note: Latin serum has been conventionally linked with Greek orós, of identical meaning, and both compared with the Sanskrit verbal base sar-, allegedly meaning " flow" in Vedic texts (hence P. Chantraine in Dictionnaire étymologique de la langue grecque). More recently, however, this interpretation has been rejected, and sar- read as "run off"—hence Vedic Sanskrit ásarat "ran off," prasísarti "lets run, stretches, extends," not akin to sáraḥ "lake, pond" and related words, which describe still water. The Sanskrit etymon has been further compared with Greek hállomai "(I) spring, hop," Latin salīre "to jump" (see sally entry 2). If this is correct the Indo-European base is *sel-, and any connection to serum and orós impossible; these two words are left then without any certain etymology.


from attributive use of serum entry 1

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serum accident

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Last Updated

12 Aug 2022

Cite this Entry

“Serum.” Dictionary, Merriam-Webster, Accessed 13 Aug. 2022.

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More Definitions for serum


se·​rum | \ ˈsir-əm How to pronounce serum (audio) \

Kids Definition of serum

: the clear liquid part that can be separated from coagulated blood and contains antibodies


se·​rum | \ ˈsir-əm How to pronounce serum (audio) \
plural sera\ -​ə How to pronounce serum (audio) \ or serums

Medical Definition of serum

 (Entry 1 of 2)

: the watery portion of an animal fluid remaining after coagulation:
a(1) : the clear yellowish fluid that remains from blood plasma after fibrinogen, prothrombin, and other clotting factors have been removed by clot formation

called also blood serum

(2) : antiserum
b : a normal or pathological serous fluid (as in a blister)



Medical Definition of serum (Entry 2 of 2)

: occurring or found in the serum of the blood serum cholesterol serum glutamic-oxaloacetic transminase

More from Merriam-Webster on serum

Thesaurus: All synonyms and antonyms for serum

Nglish: Translation of serum for Spanish Speakers

Britannica English: Translation of serum for Arabic Speakers


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