Retired permanently on grounds of ill health (9)
I believe the answer is:
bedridden
'retired permanently on grounds' is the definition.
The answer and definition are different parts of speech. However, adjectives and past participle verbs can sometimes mean the same thing.
'ill health' is the wordplay.
'ill' becomes 'bedrid' (similar in meaning).
'health' becomes 'den' (I can't explain this - if you can you should give a lot more credence to this answer).
'bedrid'+'den'='BEDRIDDEN'
'of' is the link.
Can you help me to learn more?
(Other definitions for bedridden that I've seen before include "Unwell" , "laid up" , "permanently retired" .)