Outlaw robbing a bank (3)
I believe the answer is:
ban
'outlaw' is the definition.
(banning is a kind of outlawing)
'robbing a bank' is the wordplay.
I cannot really see how this works, but
'a' could be 'an' and 'an' is present in the answer.
A single letter 'b' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ban that I've seen before include "Exile" , "Officially prohibit" , "Veto" , "Censor or proscribe" , "Hungarian governor < to forbid" .)