Misrepresent fine opinion (6)
I believe the answer is:
belief
'opinion' is the definition.
(an opinion is a personal belief)
'misrepresent fine' is the wordplay.
'misrepresent' becomes 'belie' (synonyms).
'fine' becomes 'f' (abbreviation).
'belie'+'f'='BELIEF'
(Other definitions for belief that I've seen before include "Trust, faith (6)" , "Credo" , "Conviction, faith" , "Faith, credence" , "Faith, doctrine" .)