Gloomy doctor became prominent (6)
I believe the answer is:
morose
'gloomy' is the definition.
(morose means gloomy or sad)
'doctor became prominent' is the wordplay.
I cannot really understand how this works, but
'doctor' could be 'mo' (medical officer) and 'mo' is present in the answer.
The remaining letters 'rose' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for morose that I've seen before include "Moody, glum" , "Surly and unforthcoming" , "Silent, gloomy and ill-tempered" , "Sullen and brooding" , "dark" .)