A giant one goes to a fairy queen (7)
I believe the answer is:
titania
'fairy queen' is the definition.
(I've seen this before)
'a giant one goes to a' is the wordplay.
'a giant' becomes 'titan' (titans are giant mythological creatures).
'one' becomes 'i' (Roman numeral).
'goes to' is a charade indicator (letters next to each other).
'titan'+'i'+'a'='TITANIA'
(Other definitions for titania that I've seen before include "Bottom attracts me" , "Queen of the fairies - Uranus satellite" , "Shakespeare's queen of the fairies" , "Queen of fairyland" , "Fairy Queen (MND)" .)