Comic sent up Liberal peer (5)
I believe the answer is:
droll
'comic' is the definition.
(thesaurus)
'sent up liberal peer' is the wordplay.
'sent up' says the letters should be written backwards.
'liberal' becomes 'l' (abbreviation).
'peer' becomes 'lord' (I've seen this before).
'l'+'lord'='llord'
'llord' reversed gives 'DROLL'.
(Other definitions for droll that I've seen before include "Amusing in offbeat way" , "Humorous or whimsical" , "Clownish" , "Zany" , "rum" .)