anitaircraft cannon

from The Collaborative International Dictionary of English v.0.48

Aerogun \A"["e]r*o*gun`\, n. [A["e]ro- + gun.]
   A cannon capable of being trained at very high angles for use
   against aircraft. Now usually referred to an {anitaircraft
   cannon}.
   [Webster 1913 Suppl. +PJC]