Miss a festivity (4)
I believe the answer is:
gala
'festivity' is the definition.
(gala is a kind of festivity)
'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 "Festivity - celebration" , "Swimming competition" , "sporting event" , "Festive celebration" , "Mix" .)