Bad rule may become permanent (7)
I believe the answer is:
durable
'permanent' is the definition.
(thesaurus)
'bad rule may become' is the wordplay.
'may become' is an anagram indicator.
'bad'+'rule'='badrule'
'badrule' with letters rearranged gives 'DURABLE'.
(Other definitions for durable that I've seen before include "Lasting a long time" , "Likely to last" , "Made to last" , "Capable of lasting" , "Tough and long-wearing" .)