Outlaw some mountebanks (3)
I believe the answer is:
ban
'outlaw' is the definition.
(banning is a kind of outlawing)
'some mountebanks' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'BAN' can be found hidden inside 'mountebanks'.
(Other definitions for ban that I've seen before include "Stop" , "Censor or proscribe" , "Bar, prohibition" , "'Forbid, prohibit (3)'" , "Exile" .)