Fanta's first, then open Sprite (5)
I believe the answer is:
fairy
'sprite' is the definition.
(synonyms)
'fanta's first then open' is the wordplay.
'fanta's first' becomes 'f' (1st letter of 'fanta').
'then' is a charade indicator (letters next to each other).
'open' becomes 'airy' (both can mean spacious).
'f'+'airy'='FAIRY'
(Other definitions for fairy that I've seen before include "Mythical being" , "eg Puck" , "Magical being" , "Creature of folklore" , "Cobweb, perhaps" .)