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

Overnight Reset Oil-in-SerumA medley of seed oils, including meadowfoam and sunflower, are encapsulated and float in a serum spiked with acmella oleracea extract, which is known for plumping and smoothing like Botox without any needles involved. Devon Abelman, Allure, "Somin of K-Pop Group KARD Just Shared Her Favorite Skin-Care Devices and Products," 10 Sep. 2019 Choosing a serum with packed with active ingredients like salicylic acid will help keep your skin clear and glowing on the regular. Deanna Pai, Glamour, "6 Super-Satisfying Ways to Clean Out Your Pores," 4 Sep. 2019 If so, skip the step and go straight to a serum with a high concentration of hyaluronic acid, an ingredient that’s naturally created in our bodies to help retain moisture. Andrea Cheng, Condé Nast Traveler, "The Best Skin Care Routine For Your Next Flight: A Step-By-Step Guide," 30 Aug. 2019 Go With a Serum Designed to deliver a high concentration of actives, serums are the most common form of delivery for vitamin C. Vogue, "Everything You Need to Know About Vitamin C," 19 Aug. 2019 Like Russak, Ciucci then recommends applying an SPF (ideally a lightweight serum) to cleansed skin to protect skin from the sun and serve in place of a primer. Kristen Granero, NBC News, "Sweating, chafing, chlorine: Solutions to summer's biggest hair and skin challenges," 18 Aug. 2019 The fast-absorbing Vitamin C serum brightens skin and diminishes texture. Kaitlyn Frey,, "The Beauty Products Khloé Kardashian Uses in Her Current Skincare Lineup," 27 Aug. 2019 And at nighttime, Mad Hippie Vitamin C serum and NOTO Botanics face oil. Ryan Walker-hartshorn, Bon Appétit, "Sinikiwe Dhliwayo Wants Everyone to Chill Out in Triangle Pose," 27 Aug. 2019 Peggy Carter gets the super soldier serum instead of Steve Rogers and proceeds to kick butt as Captain Carter. Jennifer Ouellette, Ars Technica, "Ewan McGregor confirms he will return as Obi-Wan for new Star Wars series," 24 Aug. 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

13 Sep 2019

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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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