Girl at a celebration (4)
I believe the answer is:
'celebration' is the definition.
(I know that celebration can be written as gala)
'girl at a' is the wordplay.
'girl' becomes 'gal' (synonyms).
'at' says to put letters next to each other.
(Other definitions for gala that I've seen before include "Prod with the elbow" , "Fête" , "Sports meeting" , "A show of charity" , "Festive entertainment" .)