(also flack ) / flæk; NAmE / noun [ U ]
1.
guns on the ground that are shooting at enemy aircraft; bullets from these guns
2.
( informal ) severe criticism :
He's taken a lot of flak for his left-wing views.
She came in for a lot of flak from the press.
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WORD ORIGIN
1930s: from German , abbreviation of Fliegerabwehrkanone , literally aviator-defence gun.