Amusing nobleman backed Liberal (5)
I believe the answer is:
Here is my best explanation:
'amusing' is the definition.
(I've seen this before)
'nobleman backed liberal' is the wordplay.
'nobleman' becomes 'lord' (synonyms).
'backed' is a reversal indicator.
'liberal' becomes 'l' (abbreviation).
'lord' in reverse letter order is 'drol'.
(Other definitions for droll that I've seen before include "Oddly amusing or comical", "rum", "Mildly amusing", "Funny", "Amusing in offbeat way", "Large amount (of matter)", "Strangely amusing", "Amusing, comical", "Clownish" and "Humorous or whimsical".)