/ Dictionary / Index T Thompson submachine gun: Meaning and Definition of Find definitions for: Thomp'son submachine' gun" Pronunciation: [key] a portable, .45-caliber, automatic weapon designed to be fired from the shoulder or hip. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Thompson seedless Thomsen Related Content Daily Word Quiz: soporific Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language