Brief downpour (6)
I believe the answer is:
shower
'brief downpour' is the definition.
(I have seen 'Short downpour ' mean 'shower' so perhaps 'downpour' could also mean 'shower'; 'brief' asks for an abbreviation)
This is the entire clue.
(Other definitions for shower that I've seen before include "Brief spell of precipitation" , "Brief rainfall" , "Plumbing fixture and brief period of precipitation" , "Lavish" , "One demonstrating" .)