Wiktionary
in a flash
a. (context idiomatic English) instantaneous, very quick, in a very short amount of time. adv. (context idiomatic English) Very quickly
WordNet
in a flash
adv. without any delay; "he was killed outright" [syn: instantaneously, outright, instantly]
Usage examples of "in a flash".
Ideas, no matter how bizarre or fallacious, can span the world in a flash.
Each man reeled away in a flash of light, with singed hair stinking and white robe burning.
Now just twenty yards away, the nose of the jet fighter suddenly erupted in a flash of fire and smoke.
The rosy wall dwindled in a flash to a point of light and disappeared!
I was beside him in a flash, but he was dead to the world, with a great ugly gash welling blood among his curls.