Amusing nobleman turning up with line (5)
I believe the answer is:
droll
'amusing' is the definition.
(I've seen this before)
'nobleman turning up with line' is the wordplay.
'nobleman' becomes 'lord' (synonyms).
'turning up' says the letters should be written in reverse.
'with' says to put letters next to each other.
'line' becomes 'l' (used when specifying particular lines from a poem).
'lord' written backwards gives 'drol'.
'drol'+'l'='DROLL'
(Other definitions for droll that I've seen before include "Oddly amusing or comical" , "Large amount (of matter)" , "rum" , "Drily amusing" , "Funny" .)