Owned ship, following lawmen with keys (9)
I believe the answer is:
possessed
'owned' is the definition.
('possess' can be a synonym of 'own')
'ship following lawmen with keys' is the wordplay.
I cannot really understand how this works, but
'ship' could be 'ss' (prefix in ship names eg SS Great Britain) and 'ss' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for possessed that I've seen before include "It's collected" , "Taken over and owned - by the devil?" , "Taken over by an evil spirit" , "Bore" , "controlled by inner demons?" .)