noun Biology.
an orientation of an organism to an external stimulus, as light, especially by growth rather than by movement.

1895–1900; independent use of -tropism

tropismatic [troh-piz-mat-ik] , adjective
tropistic [troh-pis-tik] , adjective Unabridged


variant of -tropy.

see -tropy, -ism Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
tropism (ˈtrəʊpɪzəm)
the response of an organism, esp a plant, to an external stimulus by growth in a direction determined by the stimulus
[from Greek tropos a turn]

-tropism or -tropy
n combining form
indicating a tendency to turn or develop in response to a certain stimulus: phototropism
[from Greek tropos a turn]
-tropy or -tropy
n combining form
[from Greek tropos a turn]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

1899, "tendency of an animal or plant to turn or move in response to a stimulus," abstracted from geotropism, ult. from Gk. tropos (see trope).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

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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American Heritage
Science Dictionary
tropism  [%PREMIUM_LINK%]     (trō'pĭz'əm)  Pronunciation Key 
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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Encyclopedia Britannica


response or orientation of a plant or certain lower animals to a stimulus that acts with greater intensity from one direction than another. It may be achieved by active movement or by structural alteration. Forms of tropism include phototropism (response to light), geotropism (response to gravity), chemotropism (response to particular substances), hydrotropism (response to water), thigmotropism (response to mechanical stimulation), traumatotropism (response to wound lesion), and galvanotropism, or electrotropism (response to electric current). Most tropic movements are orthotropic; i.e., they are directed toward the source of the stimulus. Plagiotropic movements are oblique to the direction of stimulus. Diatropic movements are at right angles to the direction of stimulus.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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