Crush nut noisily (7)
I believe the answer is:
conquer
'crush' is the definition.
(I've seen this before)
'nut noisily' is the wordplay.
'nut' becomes 'conker' (the nut of a horse chestnut tree).
'noisily' indicates a 'sounds like' (homophone) clue.
'conker' sounds like 'CONQUER'.
(Other definitions for conquer that I've seen before include "to follow William's example" , "Capture by force" , "Put down by force" , "Overcome militarily" , "Gain possession by force" .)