One with an occupation (6)
I believe the answer is:
tenant
'occupation' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'one with an' is the wordplay.
'one' becomes 'tent' (I can't explain this - if you can you should give a lot more credence to this answer).
'with' is an insertion indicator.
'tent' placed around 'an' is 'TENANT'.
Can you help me to learn more?
(Other definitions for tenant that I've seen before include "holder" , "Lodger" , "Someone who pays rent" , "Rent-payer" , "Person renting property" .)