[seer-uh m]
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noun, plural se·rums, se·ra [seer-uh] /ˈsɪər ə/.
  1. the clear, pale-yellow liquid that separates from the clot in the coagulation of blood; blood serum.
  2. immune serum.
  3. any watery animal fluid.
  4. the thin, clear part of the fluid of plants.
  5. milk whey.

Origin of serum

1655–65; < Latin: whey
Related formsse·rum·al, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for serum


noun plural -rums or -ra (-rə)
  1. See blood serum
  2. antitoxin obtained from the blood serum of immunized animals
  3. physiol zoology clear watery fluid, esp that exuded by serous membranes
  4. a less common word for whey
Derived Formsserumal, adjective

Word Origin for serum

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

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

serum in Medicine


n. pl. se•rums
  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.

serum in Science


Plural serums 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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.