Religious reformer is very funny, and fat (7)
I believe the answer is:
lollard
'religious reformer' is the definition.
(Lollards were a pre-Reformation Christian movement)
'very funny and fat' is the wordplay.
'very funny' becomes 'lol' (internet acronym for laugh out loud).
'and' says to put letters next to each other.
'fat' becomes 'lard' (lard is a kind of fat).
'lol'+'lard'='LOLLARD'
'is' acts as a link.
(Other definitions for lollard that I've seen before include "Wycliffite" , "Follower of John Wyclif" , "religious reformer" , "Follower of John Wycliffe" , "Radical Christian" .)