Try Our Apps


Avoid these words. Seriously.


[seer-uh m] /ˈsɪər əm/
noun, plural serums, sera
[seer-uh] /ˈsɪər ə/ (Show IPA)
the clear, pale-yellow liquid that separates from the clot in the coagulation of blood; blood serum.
any watery animal fluid.
the thin, clear part of the fluid of plants.
milk whey.
Origin of serum
1655-65; < Latin: whey
Related forms
serumal, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
Cite This Source
Examples from the Web for serum
Contemporary Examples
Historical Examples
British Dictionary definitions for serum


noun (pl) -rums, -ra (-rə)
antitoxin obtained from the blood serum of immunized animals
(physiol, zoology) clear watery fluid, esp that exuded by serous membranes
a less common word for whey
Derived Forms
serumal, adjective
Word Origin
C17: from Latin: whey
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Cite This Source
Word Origin and History for serum

1670s, "watery animal fluid," from Latin serum "watery fluid, whey," from PIE root *ser- (2) "to run, flow" (cf. Greek oros "whey;" Sanskrit sarah "flowing," sarit "brook, river"). First applied 1893 to blood serum used in medical treatments.

Online Etymology Dictionary, © 2010 Douglas Harper
Cite This Source
serum in Medicine

serum se·rum (sēr'əm)
n. pl. se·rums or se·ra (sēr'ə)

  1. A watery fluid, especially one that moistens the surface of serous membranes or that is exuded by such membranes when they become inflamed.

  2. The clear yellowish fluid obtained upon separating whole blood into its solid and liquid components.

  3. Such fluid from the tissues of immunized animals, containing antibodies and used to transfer immunity to another individual.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
Cite This Source
serum in Science
Plural serums or sera
  1. See blood serum.

  2. 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.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
Cite This Source

Word of the Day

Nearby words for serum

Difficulty index for serum

Most English speakers likely know this word

Word Value for serum

Scrabble Words With Friends