A decent reform established by law (7)
I believe the answer is:
enacted
'established by law' is the definition.
'enacted' can be an answer for 'established' (enacting is a kind of establishing). I am unsure of the 'by law' bit.
'a decent reform' is the wordplay.
'reform' indicates anagramming the letters (letters in a new form).
'a'+'decent'='adecent'
'adecent' with letters rearranged gives 'ENACTED'.
Can you help me to learn more?
(Other definitions for enacted that I've seen before include "Made a bill into law" , "A decent (anag.)" , "Ordained" , "Performed as in a play, or passed into law" , "Represented" .)