He is forced to serve in a private capacity (9)
I believe the answer is:
conscript
'he is forced to serve in a private capacity' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he is forced to serve' is the wordplay.
'he' becomes 'Con'.
'is forced to serve' becomes 'script' (I can't justify this - if you can you should believe this answer much more).
'con'+'script'='CONSCRIPT'
Can you help me to learn more?
(Other definitions for conscript that I've seen before include "Person drafted into military service" , "Enlist compulsorily" , "One enrolled" , "One compulsorily enlisted" , "Enrol for compulsory service" .)