Reduce to powder (9)
I believe the answer is:
pulverise
'reduce to powder' is the definition.
('reduce to powder'->'pulverize' is in my internal thesaurus and 'ize'->'ise')
This is the entire clue.
(Other definitions for pulverise that I've seen before include "Grind to powder" , "Reduce to dust (S, not Z)" , "Beat to a pulp" , "defeat" , "Crush thoroughly in a repulsive way" .)