Thompson

wiktionary

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Variant of Thomson, from Tom +‎ -son, originally meaning "son of Thomas". Also an anglicisation of the Gaelic name MacTamhais, meaning "son of Thomas".

etymonline

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Thompson (n.)

type of sub-machine gun, 1919, named for U.S. Gen. John T. Thompson (1860-1940), who conceived it and whose company financed it. Familiarly Tommy gun by 1929.