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
Cleanse, tone, prime, moisturise, serum, eye cream, face mist, and repeat, as children - some of them of primary-school age - seek the Korean "glass skin" look.
From BBC ● Jun. 6, 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
Baron dragged and carried McCormick to a nearby hut, sat him up on a cot, and gave him a large transfusion of blood serum from Africans who had survived Ebola.
From "The Hot Zone" by Richard Preston
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, whatever will be will be, we're going to Wembley," was how the Rovers fans serenaded their players at the end, with the team taking the acclaim.
From BBC ● Feb. 28, 2023
But the past tense of que sera sera is what used to be used to be, and growing up is getting to know it, accepting that lives move on.
From Los Angeles Times ● Jan. 25, 2023
For zuppa della sera at home, Smith says: Sauté some minced garlic for about a minute in 2 tablespoons of extra virgin olive oil.
From Seattle Times ● Oct. 1, 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
After noticing that many creators were promoting rosemary serums and rosemary-based products for better skin recovery, Pang and Rapp Reyes approached Leung to understand whether these claims had scientific merit.
From Science Daily ● Dec. 7, 2025
Jeanine has spent most of her adult life developing the serums.
From "Insurgent" 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.
