/ Dictionary / Index T thermionics: Meaning and Definition of Find definitions for: therm•i•on•ics Pronunciation: (thûrm"ī-on'iks, thûr"mē-), [key] — n. (used with a sing. v.) the branch of physics that deals with thermionic phenomena. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: thermionics (Thesaurus) thermionic current thermionic tube Related Content Daily Word Quiz: blithesome Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language