He admits vessel is freehold (9)
I believe the answer is:
ownership
'he admits' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'vessel is freehold' is the wordplay.
I cannot quite understand how this works, but
'vessel' could be 'ship' (ship is a kind of vessel) and 'ship' is located in the answer.
The remaining letters 'owner' is a valid word 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 ownership that I've seen before include "Proprietary right of possession" , "Legal title" , "Proprietorship, possession" , "The right of possessing something" .)