Doctor and diplomat overseas go brown, with time (10)
I believe the answer is:
consultant
'doctor' is the definition.
(I have seen 'Senior doctor' mean 'consultant' so perhaps 'doctor' could also mean 'consultant')
'diplomat overseas go brown with time' is the wordplay.
'diplomat overseas' becomes 'consul' (consul can mean a diplomat).
'go brown' becomes 'tan' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'time' becomes 't' (abbreviation).
'consul'+'tan'+'t'='CONSULTANT'
'and' acts as a link.
(Other definitions for consultant that I've seen before include "Adviser" , "See 1 across" , "Senior hospital doctor" , "Specialist" .)