Reveal new fun - not new (6)
I believe the answer is:
unfold
'reveal' is the definition.
(unfolding is a kind of revealing)
'new fun not new' is the wordplay.
'new' indicates anagramming the letters.
'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" .)