• synonyms


[foh-tot-n-uh s]
noun Biology.
  1. the normal condition of sensitiveness to light in organisms or their organs.
  2. the irritability exhibited by cytoplasm when exposed to light of a certain intensity.
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Origin of phototonus

First recorded in 1870–75; photo- + tonus
Related formspho·to·ton·ic [foh-tuh-ton-ik] /ˌfoʊ təˈtɒn ɪk/, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for phototonus


  1. the condition of plants that enables them to respond to the stimulus of light
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Derived Formsphototonic (ˌfəʊtəʊˈtɒnɪk), adjective

Word Origin

C19: from photo- + Greek tonos tone
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

phototonus in Medicine


  1. The state of being sensitive to or irritated by light.
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Related formspho′to•tonic (fō′tə-tŏnĭk) adj.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.