Immediate flash (7)
I believe the answer is:
instant
This clue is a double definition.
'immediate' is the first definition.
(I've seen this in another clue)
'flash' is the second definition.
(I know that flash can be written as instant)
(Other definitions for instant that I've seen before include "Sudden; moment" , "Occurring immediately, like some fast food" , "Fast, flash" , "Trice" , "Precise moment" .)