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

Definition of serum

 (Entry 1 of 2)

1 : the watery portion of an animal fluid remaining after coagulation:
a(1) : blood serum
(2) : antiserum
b : whey
c : a normal or pathological serous fluid (as in a blister)
2 : the watery part of a plant fluid
3 : 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



Definition of serum (Entry 2 of 2)

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

Examples of serum in a Sentence


The patient was administered serum.

Recent Examples on the Web: Noun

This multi-peptide serum works gently on sensitive skin, is so easy to use, and has a cult following for its all-in-one anti-aging benefits. Kelly O'sullivan, Country Living, "I'm Addicted to Anti-Aging Products and The Ordinary Is the Best Brand I've Ever Used," 13 Feb. 2019 Virtually every major beauty brand has a range of creams and serums that promise to make the skin under your eyes smooth. Shannon Romanowski, SELF, "Does Preparation H Actually Help Treat Puffy Eyes?," 28 Dec. 2018 There was always a solution for X. Exfoliator plus anti-aging cream plus serum for the anxious single teacher turning 40. Amber Sparks, The Cut, "Rediscovering Vanity, As a Mom," 21 May 2018 As the movie is set in the 1990s, the trailer also features some shots of Marvel institutions Nick Fury (Samuel L. Jackson) and Agent Coulson (Clark Gregg) after getting a dose of that wonderful CGI youth serum. Alex Abad-santos, Vox, "Why Captain Marvel punches an old lady in the Captain Marvel trailer, explained.," 18 Sep. 2018 Both allow for supreme hold without leaving your hair dry and crunchy. 4. ...or try a serum! Sam Escobar, Good Housekeeping, "17 Genius Curly Hair Tips and Tricks," 1 Dec. 2017 Use it every morning and night–before any other serums and moisturizer. The Cut, "How to Get the Most Out of Your Serum," 13 July 2018 The latest iterations, however, have smart technology — soft-focus filters, breathable textures — and skin-care-level ingredients, making them function as highlighter, serum and moisturizer in one tube. Kari Molvar, New York Times, "Modern Primers for Naturally Glowing Skin," 19 Feb. 2018 Oils, serums, and snail-mucus masks are a few of the hot categories. Elizabeth Winkler, WSJ, "What Snail Mucus Says About Beauty Trends," 26 Dec. 2018

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.

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First Known Use of serum


1665, in the meaning defined at sense 1


1876, in the meaning defined above

History and Etymology for serum


Latin, whey, wheylike fluid; akin to Greek oros whey

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Statistics for serum

Last Updated

15 Mar 2019

Look-up Popularity

Time Traveler for serum

The first known use of serum was in 1665

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English Language Learners Definition of serum

medical : the part of blood that is like water and that contains substances (called antibodies) that fight disease
medical : serum from an animal's blood that can be added to a person's blood to prevent or cure disease
biology : the watery part of a fluid found in a plant


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 sera (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

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More from Merriam-Webster on serum

Rhyming Dictionary: Words that rhyme with serum

Spanish Central: Translation of serum

Nglish: Translation of serum for Spanish Speakers

Britannica English: Translation of serum for Arabic Speakers

Comments on serum

What made you want to look up serum? Please tell us where you read or heard it (including the quote, if possible).


to corrupt or become corrupted

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