ack-ack
/ˌækˈæk/noun
1- Military, informal an anti-aircraft gun or regiment【军】〈非正式〉高射炮; 防空部队。
1.1
- mass noun anti-aircraft gunfire高射炮火。
词源
signallers' name for the letters AA; ack for A was replaced in military use by able in 1942.