Coupled prisoner and prison were worrying (9)
I believe the answer is:
conjugate
'coupled' is the definition.
('conjugate' can be a synonym of 'coupled')
'prisoner and prison were worrying' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'and' is a charade indicator (letters next to each other).
'prison' becomes 'jug'.
'were worrying' becomes 'ate' (I can't explain this - if you can you should give a lot more credence to this answer).
'con'+'jug'+'ate'='CONJUGATE'
Can you help me to learn more?
(Other definitions for conjugate that I've seen before include "State the various parts of a verb" , "Connected with" , "go through forms of torture, perhaps?" , "Joined" , "Give different forms of (a verb)" .)