/ Dictionary / Index T thermionic valve: Meaning and Definition of Find definitions for: therm'ion'ic valve' Pronunciation: [key] — Brit. Brit. See Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. thermionic tube thermistor Related Content Daily Word Quiz: impetuous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language