Opening of fete, not just an amusement park (7)
I believe the answer is:
funfair
'amusement park' is the definition.
(synonyms)
'opening of fete not just' is the wordplay.
'opening of' says to take the initial letters.
'not just' becomes 'unfair' ('unfair' is the opposite to 'just').
The first letter of 'fete' is 'f'.
'f'+'unfair'='FUNFAIR'
'an' is the link.
(Other definitions for funfair that I've seen before include "Amusements here" , "Swings and roundabouts" , "Amusement park" , "entertainment for the family?" , "place of amusement" .)