Possibly one-armed villain (6)
I believe the answer is:
bandit
'villain' is the definition.
(thesaurus)
'possibly one-armed' is the wordplay.
I cannot quite see how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for bandit that I've seen before include "Armed brigand" , "Outlaw, brigand" , "Member of a gang of robbers" , "Armed outlaw" , "Member of a robber gang" .)