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.
Entries linking to thompson
Tommy
"British soldier," 1884, from Thomas Atkins, since 1815 the typical sample name for filling in army forms. Tommy gun (1929) is short for Thompson gun (see Thompson). Soon extended to other types of sub-machine gun, especially those favored by the mob.