Relating to a noble (5)
I believe the answer is:
ducal
'relating to a noble' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ducal that I've seen before include "Relating to the highest British hereditary title" , "Relating to a nobleman" , "Relating to some nobles" , "Relating to a high peer" , "High-ranking" .)