[op-er-too-nis-tik, -tyoo-]


adhering to a policy of opportunism; practicing opportunism.
  1. (of a microorganism) causing disease only under certain conditions, as when a person's immune system is impaired.
  2. (of a disease or infection) caused by such an organism: Pneumocystis pneumonia is an opportunistic disease that often strikes victims of AIDS.

Origin of opportunistic

First recorded in 1890–95; opportunist + -ic
Related formsop·por·tun·is·ti·cal·ly, adverbun·op·por·tun·is·tic, adjective
Can be confusedopportune opportunistic
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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British Dictionary definitions for opportunistic



of or characterized by opportunism
med (of an infection) caused by any microorganism that is harmless to a healthy person but debilitates a person whose immune system has been weakened by disease or drug treatment
Derived Formsopportunistically, adverb
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 opportunistic

1889, see opportunist + -ic. Related: Opportunistically.

Online Etymology Dictionary, © 2010 Douglas Harper

opportunistic in Medicine




Of or relating to an organism capable of causing disease only in a host whose resistance is lowered.
Of or relating to a disease caused by an opportunistic organism.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.