serum
Americannoun
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serums,
plural
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sera
plural
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the clear, pale-yellow liquid that separates from the clot in the coagulation of blood; blood serum.
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any watery animal fluid.
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the thin, clear part of the fluid of plants.
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milk whey.
noun
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See blood serum
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antitoxin obtained from the blood serum of immunized animals
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physiol zoology clear watery fluid, esp that exuded by serous membranes
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a less common word for whey
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serums
plural
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See blood serum
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Blood serum extracted from an animal that has immunity to a particular disease. The serum contains antibodies to one or more specific disease antigens, and when injected into humans or other animals, it can transfer immunity to those diseases.
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Etymology
Origin of serum
1655–65; < Latin: whey
Explanation
Technically, serum is the part of blood that doesn’t clot, or any kind of “watery animal fluid.” But serum as skincare refers to watery fluid made of almost anything designed to make skin more beautiful. No animals involved. The medical term serum is used to describe the watery component of blood that's left behind when blood clots or coagulates. The serum of someone who's recovered from a disease is sometimes used to treat patients who fall ill with the same disease. Antibodies in the serum can fight off the virus or bacteria that caused the illness. In Latin, serum means "watery fluid." That’s what cosmetic companies have in mind when they sell various face serums.
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
Of the successful claims, two of the men were cleared by DNA evidence, while blood serum evidence was used to prove innocence in the third.
From Salon ● Aug. 10, 2026
Also, according to Weiss, testosterone injections can cause “aggressive behavior and mood swings, especially during peak serum levels.”
From Slate ● Jul. 16, 2026
Patients with severe aortic stenosis had higher serum levels of serotonin and its primary breakdown product.
From Science Daily ● Jul. 12, 2026
In December, European-based Cosmo Pharmaceuticals reported results from a late-stage study of a serum that blocks the hormone driving hair loss directly at the scalp, without entering the bloodstream.
From The Wall Street Journal ● May 1, 2026
There’s only one place that could be: Candor headquarters, where I succumbed to the truth serum.
From "Allegiant" by Veronica Roth
The "Manana sera bonito" singer is the first Latina artist to headline the festival, which draws massive crowds over two consecutive weekends in Indio, California.
From Barron's ● Apr. 12, 2026
"Que sera, sera," quipped Postecoglou as he ended his victory news conference.
From BBC ● May 21, 2025
“It’s kind of my take on ‘it is what it is,’ ‘lo que sera sera’ kind of thing,” Apollo told ABC News of the album’s title.
From Los Angeles Times ● Jun. 6, 2024
Giffords’ response was “Sera, sera,” referencing the song “Que sera, sera” or “What will be, will be.”
From Seattle Times ● Jun. 23, 2022
“Oh, qu’elle y sera mal—peu comfortable! And her clothes, they will wear out: how can she get new ones?”
From "Jane Eyre" by Charlotte Brontë
Korean face masks and serums promising glass skin have made “K-Beauty” a multibillion-dollar industry.
From The Wall Street Journal ● Aug. 17, 2026
Afghanistan already produces a variety of serums including antibiotics, according to manufacturer Milli Shifa Pharmaceutical.
From Barron's ● Feb. 16, 2026
Dr Bhate also looked at the ingredients lists for two serums with similar branding, one from a luxury skincare brand and one from a supermarket.
From BBC ● Dec. 13, 2025
People invest significant time and effort into keeping their skin looking young through masks, creams and serums.
From Science Daily ● Nov. 29, 2025
“I’ve worked on serums too, as an Erudite.”
From "Allegiant" by Veronica Roth
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
