[ thurm-ahy-uh n, -on; thur-mee-uh n ]
/ ˈθɜrmˌaɪ ən, -ɒn; ˈθɜr mi ən /

noun Physics.

an ion emitted by incandescent material.

Origin of thermion

First recorded in 1910–15; therm- + ion


therm·i·on·ic, adjectivetherm·i·on·i·cal·ly, adverb Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for thermionic

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

    The Tower of Oblivion|Oliver Onions
  • Above the mantel of the lodge's thermionic fireplace was hung a brilliant cascading stereo of Yosemite Falls in misty motion.

    Deepfreeze|Robert Donald Locke

British Dictionary definitions for thermionic (1 of 2)

/ (ˌθɜːmɪˈɒnɪk) /


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

British Dictionary definitions for thermionic (2 of 2)

/ (ˈθɜːmɪən) /


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

Scientific definitions for thermionic

[ thûrmī′ən ]

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.