/ Dictionary / Index T thermion: Meaning and Definition of Find definitions for: therm•i•on Pronunciation: (thûrm'ī"un, -on thûr'mē&sylpun), [key] — n. Physics. an ion emitted by incandescent material. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: thermion (Thesaurus) Thermidorian thermionic current Related Content Daily Word Quiz: ravenous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language