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' suggests taking the first letters.
'not just' becomes 'unfair' ('unfair' is the opposite to 'just').
The initial letter of 'fete' is 'f'.
'f'+'unfair'='FUNFAIR'
'an' acts as a 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" .)