Witty nobleman reversed line (5)
I believe the answer is:
droll
'witty' is the definition.
(I've seen this in another clue)
'nobleman reversed line' is the wordplay.
'nobleman' becomes 'lord' (synonyms).
'reversed' says the letters should be written backwards.
'line' becomes 'l' (used when specifying particular lines from a poem).
'lord' back-to-front is 'drol'.
'drol'+'l'='DROLL'
(Other definitions for droll that I've seen before include "rum" , "Amusing - jester" , "Quaintly amusing" , "Amusing in offbeat way" , "amusing, in a strange way" .)