thermion

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An electrically charged particle, especially an electron, emitted by a conducting material at high temperatures.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics An electrically charged particle, either an electron or an ion, emitted by a conducting material at high temperatures

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an electrically charged particle (electron or ion) emitted by a substance at a high temperature