Miss a festive occasion (4)
I believe the answer is:
gala
'festive occasion' is the definition.
(thesaurus)
'miss a' is the wordplay.
'miss' becomes 'gal' ('gal' can be a synonym of 'miss').
'gal'+'a'='GALA'
(Other definitions for gala that I've seen before include "fair" , "Prod with the elbow" , "field day" , "A show of charity" , "Sports meeting" .)