Rebel first past a vault (9)
I believe the answer is:
anarchist
'rebel' is the definition.
(thesaurus)
'first past a vault' is the wordplay.
'first' becomes 'ist' (ist resembles 1st).
'past' is a charade indicator (letters next to each other).
'a' becomes 'an'.
'vault' becomes 'arch' (I've seen this in another clue).
'an'+'arch'='anarch'
'ist' after 'anarch' is 'ANARCHIST'.
(Other definitions for anarchist that I've seen before include "revolutionary" , "supporter of lawlessness" , "One who wishes to abolish all government" , "One opposing government" , "bolshevik" .)