Swanky party (4)
'swanky party' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gala that I've seen before include "Festivity - celebration" , "Festive entertainment" , "Special social or sporting occasion" , "Festive event" , "Festive occasion - variety of apple" .)
(Other definitions for soiree that I've seen before include "Evening function" , "Party assembled in the evening" , "Cultural at-home" , "A social gathering in the evening" .)