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:
“When we heard our voices, it was like injecting some kind of serum into your veins,” Parton said of the project.
From The Wall Street Journal ● Aug. 25, 2026
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
The ASA also said that the serum was tested in a different climate to the UK, and may not work similarly.
From BBC ● Apr. 28, 2026
“Pain can’t make me tell you. Truth serum can’t make me tell you. Simulations can’t make me tell you. I’m immune to all three.”
From "Insurgent" 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
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
On social media, vacationers are showing off their “pharmacy hauls” from across the continent, extolling the virtues of E.U.-made creams and serums and turning drugstores into can’t-miss destinations.
From The Wall Street Journal ● Aug. 14, 2026
Soon I was using prescription shampoo, two topical serums, monthly steroid scalp injections, and a pricey red-light therapy cap that made me look like an alien.
From Slate ● May 23, 2026
Afghanistan already produces a variety of serums including antibiotics, according to manufacturer Milli Shifa Pharmaceutical.
From Barron's ● Feb. 16, 2026
Who would have thought serums infused with snail mucin - the sticky substance they secrete - would become a part of skincare routines around the world?
From BBC ● Jan. 2, 2026
She knew that she would need to control large groups of people in order to stay secure, so she developed a way to do it with serums and transmitters.
From "Divergent" by Veronica Roth
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