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[troh-piz-uh m]
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noun Biology.
  1. 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 formstro·pis·mat·ic [troh-piz-mat-ik] /ˌtroʊ pɪzˈmæt ɪk/, adjectivetro·pis·tic [troh-pis-tik] /troʊˈpɪs tɪk/, adjective


  1. variant of -tropy.

Origin of -tropism

see origin at -tropy, -ism
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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.

British Dictionary definitions for tropism


  1. the response of an organism, esp a plant, to an external stimulus by growth in a direction determined by the stimulus
Derived Formstropismatic, adjectivetropistic (trəʊˈpɪstɪk), adjective

Word Origin

from Greek tropos a turn



n combining form
  1. indicating a tendency to turn or develop in response to a certain stimulusphototropism

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

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

tropism in Medicine


  1. The turning or bending movement of a living organism or part toward or away from an external stimulus, such as light, heat, or gravity.
Related formstropic, tro•pistic adj.


  1. Tropism:stereotropism.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

tropism in Science


  1. 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.
Related formstropistic adjective
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.