Regarding careers, you share the same concern with him (2-6)
I believe the answer is:
co-worker
'regarding careers you share the same concern with him' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'with him' is the wordplay.
I cannot really understand how this works, but
'with' could be 'w' (abbreviation) and 'w' is found within the answer.
'him' could be 'ker' and 'ker' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for co-worker that I've seen before include "Fellow employee" , "Colleague - associate" .)