Rose rambling over doctor's grave (6)
I believe the answer is:
sombre
'grave' is the definition.
(I've seen this before)
'rose rambling over doctor's' is the wordplay.
'rambling' indicates anagramming the letters.
'over' means one lot of letters goes inside another.
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus).
'rose' anagrammed gives 'sore'.
'sore' placed around 'mb' is 'SOMBRE'.
(Other definitions for sombre that I've seen before include "Dull, gloomy" , "Solemn and grave" , "Dark, serious, gloomy" , "Melancholic" , "Dark, solemn" .)