Giant, one primarily attending a fairy queen (7)
I believe the answer is:
titania
'a fairy queen' is the definition.
(I've seen this in another clue)
'giant one primarily attending' is the wordplay.
'giant' becomes 'titan' (titans are giant mythological creatures).
'one' becomes 'i' (Roman numeral).
'primarily' suggests taking the first letters.
The initial letter of 'attending' is 'a'.
'titan'+'i'+'a'='TITANIA'
(Other definitions for titania that I've seen before include "in the D [DREAM] ..." , "Bottom fan" , "Shakespeare's fairy queen" , "Oberon's queen (MND)" , "Bottom attracts me" .)