Stance in reforms, most prudent (8)
I believe the answer is:
canniest
'most prudent' is the definition.
(I've seen this in another clue)
'stance in reforms' is the wordplay.
'reforms' indicates anagramming the letters.
'stance'+'in'='stancein'
'stancein' anagrammed gives 'CANNIEST'.
(Other definitions for canniest that I've seen before include "Instance (anag)" , "Shrewdest sort of ancients" .)