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

The Deal: Sunday Riley's Game Changer Kit — which includes a full-sized Good Genes serum and Ceramic Slip cleanser — normally retails for $140, but will be on sale for $98 during Prime Days., "The Pro's Guide To The Best Beauty Haul For Amazon Prime Day," 15 July 2019 Both men received serum and medical care and recovered fully with no lingering effects. Tom Stienstra,, "Rattlesnake season is here. Be prepared.," 28 June 2019 High in vitamin C and ascorbic acid this serum is fast acting on acne scars, dark spots, and hyperpigmentation and will have your skin ready for summer. Essence Staff, Essence, "Dope Stuff On My Desk," 27 June 2019 Similarly, better insulin sensitivity and beta cell function were associated with the highest serum 25(OH)D quartile (≥34.9 ng/mL). Mackie Shilstone,, "Vitamin D reduces risk to fat gain in old age," 19 June 2019 Prices run from $1.80 for a sheet mask to $70 for an anti-aging serum. Kavita Daswani,, "Sun Becomes Her label offers new women’s styles fit for summer," 5 June 2019 This serum is supposed to support your skin's suppleness and youthful radiance using its powerful blend of retinol and lipids. Maya Allen, Marie Claire, "I Tried Meghan Markle’s Favorite Beauty Products—Here’s What’s Worth Your Money," 24 May 2019 This serum should go on during the day time, because vitamin C helps your SPF work its hardest. Meagan Fredette, Teen Vogue, "Does KylieSkin Care Live Up To The Hype?," 22 May 2019 April 2, 2019 Readers are also slamming Kourtney, who once mocked Kim for losing a diamond earring, for suggesting hundreds of dollars in serums and candles while branding herself as an everyday single mother. Sara Rodrigues, House Beautiful, "Kourtney Kardashian's Poosh Shows You How to Update Your Bathroom for Spring—for $5,700," 4 Apr. 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

19 Jul 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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