Not free to rent cargo space on board (9)
I believe the answer is:
leasehold
'not free' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'rent cargo space on board' is the wordplay.
I cannot really see how this works, but
'rent' could be 'lease' (I've seen this before) and 'lease' is found in the answer.
'cargo space' could be 'hold' (I've seen this in another clue) and 'hold' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'to' acts as a link.
Can you help me to learn more?
(Other definitions for leasehold that I've seen before include "property that's let" , "Type of tenure" , "Form of property tenure" , "Rented land" , "housing agreement" .)