Luhrmann took many seconds, subsuming sound of big gun (7)
I believe the answer is:
bazooka
'big gun' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for bazooka that I've seen before include "Anti-tank rocket launcher - trumpet-shaped kazoo" , "powerful weapon" , "Portable anti-tank weapon" , "Anti-tank gun" , "A portable rocket-launcher" .)