Amusing nobleman turning up with line (5)
I believe the answer is:
droll
'amusing' is the definition.
(I've seen this in another clue)
'nobleman turning up with line' is the wordplay.
'nobleman' becomes 'lord' (synonyms).
'turning up' says the letters should be written backwards.
'with' means one lot of letters go next to another.
'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" .)