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[troh-piz-uh m] /ˈtroʊ pɪz əm/
noun, Biology.
an orientation of an organism to an external stimulus, as light, especially by growth rather than by movement.
Origin of tropism
First recorded in 1895-1900; independent use of -tropism
Related forms
[troh-piz-mat-ik] /ˌtroʊ pɪzˈmæt ɪk/ (Show IPA),
[troh-pis-tik] /troʊˈpɪs tɪk/ (Show IPA),


variant of -tropy.
See origin at -tropy, -ism Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for tropism
Contemporary Examples
Historical Examples
  • The workers, on the other hand, who have to be in and out of the nest about their business, do not have this tropism.

    Natural Wonders Edwin Tenney Brewster
  • The object of the tropism is to keep the males and females in the nest until swarming time, and then to get them out.

    Natural Wonders Edwin Tenney Brewster
  • Driesch has found that a tropism underlies the arrangement of the skeleton in the pluteus larvae of the sea-urchin.

    Darwin and Modern Science A.C. Seward and Others
  • As a type of human behavior it may be explained, like the attraction of the flame for the moth, as a sort of tropism.

  • This may be a tropism (stereotropism) or it may be a mere surface tension phenomenon.

  • We shall in the succeeding series of papers deal with the subject of tropism in general.

British Dictionary definitions for tropism


the response of an organism, esp a plant, to an external stimulus by growth in a direction determined by the stimulus
Derived Forms
tropismatic, adjective
tropistic (trəʊˈpɪstɪk) adjective
Word Origin
from Greek tropos a turn


combining form
indicating a tendency to turn or develop in response to a certain stimulus: phototropism
Word Origin
from Greek tropos a turn
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
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Word Origin and History for tropism

1899, "tendency of an animal or plant to turn or move in response to a stimulus," abstracted from geotropism, ultimately from Greek tropos (see trope).

Online Etymology Dictionary, © 2010 Douglas Harper
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tropism in Medicine

tropism tro·pism (trō'pĭz'əm)
The turning or bending movement of a living organism or part toward or away from an external stimulus, such as light, heat, or gravity.

tro'pic, tro·pis'tic adj.

-tropism suff.
Tropism: stereotropism.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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tropism in Science
The growth or movement of a living organism or anatomical structure toward or away from an external stimulus, such as light, heat, or gravity. See also geotropism, hydrotropism, phototropism.

tropistic adjective
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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