He quits for a job at eastern syndicate (8)
I believe the answer is:
apostate
'he quits' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a job at eastern syndicate' is the wordplay.
'job' becomes 'post' (post is a kind of job).
'eastern syndicate' becomes 'e' (I can't explain this - if you can you should believe this answer much more).
'a'+'post'+'at'+'e'='APOSTATE'
'for' is the link.
Can you help me to learn more?
(Other definitions for apostate that I've seen before include "Person who renounces former belief or loyalty" , "heretic" , "Deserter" , "Julian was such" , "Turncoat" .)