serum
Americannoun
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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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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:
Also, according to Weiss, testosterone injections can cause “aggressive behavior and mood swings, especially during peak serum levels.”
From Slate ● Jul. 16, 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
An advert for a £49 face serum has been banned over misleading claims that it made users look up to five years younger.
From BBC ● Apr. 28, 2026
Detecting such a strong signal from just 1 milliliter of serum was unexpected.
From Science Daily ● Feb. 17, 2026
Matthew inoculates people against the memory serum all throughout the day, Cara and Caleb and Tris and Nita and Reggie and himself.
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
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
Young shoppers enamored with the “glass skin” look are snapping up serums, peels, gels and mists.
From The Wall Street Journal ● May 28, 2026
Afghanistan already produces a variety of serums including antibiotics, according to manufacturer Milli Shifa Pharmaceutical.
From Barron's ● Feb. 16, 2026
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
Ironically, years of dermatology visits and pricey serums hadn’t managed what a $3 tub of yogurt did in weeks.
From Slate ● Feb. 22, 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.
