He is working for commission (5)
I believe the answer is:
cadet
'he is working for commission' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he is working for commission' is the wordplay.
'he' becomes 'Cad'.
'is working for commission' becomes 'et' (I can't explain this - if you can you should believe this answer much more).
'cad'+'et'='CADET'
Can you help me to learn more?
(Other definitions for cadet that I've seen before include "Police force trainee" , "Officer-trainee" , "Military trainee officer" , "aspiring officer" , "Apprentice officer" .)