Giant, one meeting a fairy queen (7)
I believe the answer is:
Here is my best explanation:
'fairy queen' is the definition.
(I've seen this before)
'giant one meeting a' is the subsidiary indication.
'giant' becomes 'titan' ('titan' can be a synonym of 'giant'**).
'one' becomes 'i' (roman numeral).
'meeting' says to put letters next to each other.
(Other definitions for titania that I've seen before include "Oberon's queen (MND)", "Queen of the fairies - Uranus satellite", "Oberon's better half?", "Wife of Oberon (MND)", "Queen of fairyland", "Shakespeare's queen of the fairies", "Fairy queen (AMND)", "Shakespeare's fairy queen", "Queen of the Fairies" and "Fairy Queen (MND)".)