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

Indulge in a facial, massage, or illuminating peel, then peruse the bounty of natural and organic salves and serums in the apothecary. Taylore Glynn, Marie Claire, "Your Beauty Guide to Albuquerque," 3 May 2019 Add some hair serum to keep your hair smooth all night. Alanna Greco, Seventeen, "Exactly What to Wear to Prom, According to Your Sign," 11 Mar. 2019 Belei's first drop is entirely skin care essentials like face wipes, moisturizers, and serums; this being Amazon, the prices stick between $9 and $40. Glamour, "Amazon Just Launched Its Own Skin Care Line, and Everything Is Under $40," 20 Mar. 2019 Instead, grab a serum or moisturizer high in green tea—often listed as camellia sinensis leaf extract on ingredients lists—and slather that on, instead. Chloe Metzger, Marie Claire, "What Do Antioxidants Really Do for Your Skin?," 20 July 2018 For those that can't make it into her midtown clinic Dangene recently launched a three-step system, consisting of an oxygen cleanser, a spray-on serum, and a moisturizer, meant for all skin types. Katheryn Erickson, Town & Country, "Beauty Address: Dangene's Institute of Skinovation," 16 Feb. 2014 Things get much more complicated with serums, creams and toners. Jenna Rosenstein, Harper's BAZAAR, "Instagram Beauty Sensation @Gelcream Shares Her Anti-Aging Secrets," 6 Mar. 2019 Based in New York City and a mother of two, Engelman talked to the Cut about her love for one very famous acid solution, the importance of an antioxidant serum, and starting retinoid again after just having a baby. Kathleen Hou, The Cut, "A Celebrity Dermatologist’s Science-Based Skin-Care Routine," 12 July 2018 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

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

10 May 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

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