Giant beginning to intimidate a fairy (7)
I believe the answer is:
titania
'fairy' is the definition.
(thesaurus)
'giant beginning to intimidate a' is the wordplay.
'giant' becomes 'titan' ('titan' can be a synonym of 'giant').
'beginning to' indicates taking the first letters.
The first letter of 'intimidate' is 'i'.
'titan'+'i'+'a'='TITANIA'
(Other definitions for titania that I've seen before include "Shakespeare's fairy queen" , "asinine lover" , "Oberon's queen (MND)" , "Shakespeare's queen of the fairies" , "Wife of Oberon (MND)" .)