flak (n.)youdaoicibaDictYouDict[flak 词源字典]
1938, "anti-aircraft gun," from German Flak, condensed from Fliegerabwehrkanone, literally "pilot warding-off cannon." Sense of "anti-aircraft fire" is from 1940; metaphoric sense of "criticism" is c. 1963 in American English. Flak jacket is by 1956.[flak etymology, flak origin, 英语词源]