plural sera
ˈsir-ə 
or serums
or serums
1
: the watery, clear portion of an animal fluid:
a
: the clear, yellowish fluid that remains from blood plasma after clotting factors (such as fibrinogen and prothrombin) have been removed by clot formation : blood serum compare antiserum, convalescent serum
b
: a normal or pathological serous fluid (as in a blister)
c
: whey
2
: 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
3
: the watery part of a plant fluid
Latex. This, the natural product of the rubber tree, is a suspension of rubber droplets in a watery serum concentrated and stabilized in such a way that the dry rubber content is between 60 and 70 per cent.—
C. A. O'Flaherty
see also truth serum
C. A. O'Flaherty
: occurring or found in the blood serum
serum cholesterol
serum antibodies
Examples of serum in a Sentence
Noun
The patient was administered serum.
Recent Examples on the WebJeannette Neumann, Fortune, 10 Apr. 2024
Editor's Tip: Allure commerce writer Jennifer Hussein says this serum is her go-to when her complexion looks more uneven than usual.
—Jennifer Hussein, Allure, 10 Apr. 2024
And this shape is perfect for applying eye creams and serums.
—Jenn Barthole, Glamour, 9 Apr. 2024
The best anti-aging ingredients for 15- or 16-year-olds to start using are antioxidants, vitamin C serums, and retinoids.
—Leslie Baumann, Miami Herald, 6 Apr. 2024
From the makeup remover balm to the serum, drops are nourishing, hydrating, and gentle on your skin.
—Alexandra Domrongchai, Travel + Leisure, 28 Mar. 2024
Bloody or brown discharge and discharge that looks like serum are additional signs of abnormal discharge.63
Causes
Intraductal papillomas are a common cause of abnormal discharge.
—Ashley Abramson, Health, 24 Mar. 2024
This serum, which targets hyperpigmentation, is an undisputed standout.
—Perrie Samotin, Glamour, 29 Mar. 2024
After testing this serum, our skin texture appeared much softer and smoother with a more radiant finish.
—Jessie Quinn, Peoplemag, 25 Mar. 2024
Charmaine Patterson, Peoplemag, 24 Oct. 2022
Noun
The serum is too harsh for thousands of the brand’s preadolescent fans — the exact demographic that founder Eisenman said has been buying more in the past six months, helping drive Bubble’s expansion into 12,000 stores in the US and the UK.
—Jeannette Neumann, Fortune, 10 Apr. 2024
Editor's Tip: Allure commerce writer Jennifer Hussein says this serum is her go-to when her complexion looks more uneven than usual.
—Jennifer Hussein, Allure, 10 Apr. 2024
And this shape is perfect for applying eye creams and serums.
—Jenn Barthole, Glamour, 9 Apr. 2024
The best anti-aging ingredients for 15- or 16-year-olds to start using are antioxidants, vitamin C serums, and retinoids.
—Leslie Baumann, Miami Herald, 6 Apr. 2024
From the makeup remover balm to the serum, drops are nourishing, hydrating, and gentle on your skin.
—Alexandra Domrongchai, Travel + Leisure, 28 Mar. 2024
Bloody or brown discharge and discharge that looks like serum are additional signs of abnormal discharge.63
Causes
Intraductal papillomas are a common cause of abnormal discharge.
—Ashley Abramson, Health, 24 Mar. 2024
This serum, which targets hyperpigmentation, is an undisputed standout.
—Perrie Samotin, Glamour, 29 Mar. 2024
After testing this serum, our skin texture appeared much softer and smoother with a more radiant finish.
—Jessie Quinn, Peoplemag, 25 Mar. 2024
Adjective
Lizzo completes her skincare process with a serum facial sheet mask from Cicapair.
—Charmaine Patterson, Peoplemag, 24 Oct. 2022
These examples are programmatically compiled from various online sources to illustrate current usage of the word 'serum.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.
Dictionary Entries Near serum
Cite this Entry
“Serum.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/serum. Accessed 16 Apr. 2024.
Copy CitationMedical Definition
serum
1 of 2 noun
se·rum
ˈsir-əm
plural sera
-ə
or serums
or serums
: 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)
b
: a normal or pathological serous fluid (as in a blister)
serum
2 of 2 adjective
: occurring or found in the serum of the blood
serum cholesterol
serum glutamic-oxaloacetic transminase
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