Come down with sombre nobleman (9)
I believe the answer is:
landgrave
'nobleman' is the definition.
(I know that landgrave is a type of Count)
'come down with sombre' is the wordplay.
'come down' becomes 'land' (to land is to come down after flying).
'with' is a charade indicator (letters next to each other).
'sombre' becomes 'grave' (I've seen this before).
'land'+'grave'='LANDGRAVE'
(Other definitions for landgrave that I've seen before include "Old count" , "high-ranking German" , "German ruler" , "Count c" , "German count" .)