Those courtly London nobles (5)
I believe the answer is:
earls
'nobles' is the definition.
(earl is a kind of noble)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for earls that I've seen before include "They're below marquess and above viscount" , "Peers of the realm" , "members of the House of Lords" , "Nobles" , "counts" .)