[thurm-ahy-uh n, -on; thur-mee-uh n]

noun Physics.

an ion emitted by incandescent material.

Origin of thermion

First recorded in 1910–15; therm- + ion
Related formstherm·i·on·ic, adjectivetherm·i·on·i·cal·ly, adverb Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Related Words for thermionic

computerized, anodic, cathodic, voltaic

Examples from the Web for thermionic

Historical Examples of thermionic

  • Above the mantel of the lodge's thermionic fireplace was hung a brilliant cascading stereo of Yosemite Falls in misty motion.


    Robert Donald Locke

  • I have even made an attempt to understand the mystery that is called the Thermionic Valve.

British Dictionary definitions for thermionic



of, relating to, or operated by electrons emitted from materials at high temperaturesa thermionic valve



physics an electron or ion emitted by a body at high temperature
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

thermionic in Science



An electrically charged particle or ion that is emitted by a heated conducting material. The electrons emitted from the cathodes of electron tubes (such as cathode ray tubes) are thermions.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.