Prohibit German sound (4)
I believe the answer is:
bang
'sound' is the definition.
(bang is a kind of sound)
'prohibit german' is the wordplay.
'prohibit' becomes 'ban' (banning is a kind of prohibiting).
'german' becomes 'g' (abbreviation).
'ban'+'g'='BANG'
(Other definitions for bang that I've seen before include "Sudden noise; fringe" , "drug injection" , "Slam" , "Strike violently" , "Hairstyle" .)