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 "in the D [DREAM] ...", "asinine lover", "Queen of fairyland", "Queen of the fairies - Uranus satellite", "Shakespeare's queen of the fairies", "Oberon's queen (MND)", "Fairy Queen (MND)", "Bottom fan", "Oberon's better half?" and "Wife of Oberon (MND)".)