Reveal new fun - not new (6)
I believe the answer is:
unfold
'reveal' is the definition.
(I know that unfold is a kind of reveal)
'new fun not new' is the wordplay.
'new' indicates an anagram.
'not new' becomes 'old' ('old' is the opposite to 'new').
'fun' is an anagram of 'unf'.
'unf'+'old'='UNFOLD'
(Other definitions for unfold that I've seen before include "Open out - develop" , "Spread out - reveal gradually" , "'O clouds, - - !' (Blake)" , "Reveal - clarify" , "Open out or reveal gradually" .)