[foh-tot-n-uh s]

noun Biology.

the normal condition of sensitiveness to light in organisms or their organs.
the irritability exhibited by cytoplasm when exposed to light of a certain intensity.

Origin of phototonus

First recorded in 1870–75; photo- + tonus
Related formspho·to·ton·ic [foh-tuh-ton-ik] /ˌfoʊ təˈtɒn ɪk/, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for phototonus



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

Word Origin for phototonus

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




The state of being sensitive to or irritated by light.
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.