Young woman attends a festivity (4)
I believe the answer is:
gala
'festivity' is the definition.
(I know that festivity can be written as gala)
'young woman attends a' is the wordplay.
'young woman' becomes 'gal' (synonyms).
'attends' means one lot of letters go next to another.
'gal'+'a'='GALA'
(Other definitions for gala that I've seen before include "Sports meeting" , "Carnival, celebration" , "Festive celebration" , "Special sports event" , "Festive performance" .)