An Etymological Dictionary of the German Language/Annotated/Geschoß
Geschoß, neuter, ‘shot, missile, dart,’ even Middle High German geschoȥ, Old High German giscoȥ, neuter, akin to schießen. So too Geschütz, ‘artillery, ordnance,’ even in Middle High German geschütze, neuter, ‘arms, weapons for shooting,’ occurs as a collective of Geschoß.