noun Immunology.
  1. a constituent of normal or immune blood serum that makes invading bacteria more susceptible to the destructive action of the phagocytes.

Origin of opsonin

1900–05; < Latin opsōn(ium) victuals (< Greek opsōnía, derivative of opsōneîn to buy provisions) + -in2
Related formsop·so·noid, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for opsonin

Historical Examples of opsonin

  • In the case of diphtheria, the antitoxin appears to be more efficacious than an opsonin.

  • Opsonin is what you butter the disease germs with to make your white blood corpuscles eat them.

    The Doctor's Dilemma

    George Bernard Shaw

  • The "opsonin," or "relish," is something exuded into or produced in the blood fluid when the attacking microbe arrives.

    More Science From an Easy Chair

    Sir E. Ray (Edwin Ray) Lankester

British Dictionary definitions for opsonin


  1. a constituent of blood serum that renders invading bacteria more susceptible to ingestion by phagocytes in the serum
Derived Formsopsonic (ɒpˈsɒnɪk), adjective

Word Origin for opsonin

C20: from Greek opsōnion victuals
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

opsonin in Medicine


  1. An antibody in blood serum that causes bacteria or other foreign cells to become more susceptible to the action of phagocytes.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.