Festival held for knight (7)
I believe the answer is:
galahad
'for knight' is the definition.
(Arthurian knight)
'festival held' is the wordplay.
'festival' becomes 'gala' (a gala is a festival or party).
'held' becomes 'had' ('have' can be a synonym of 'hold').
'gala'+'had'='GALAHAD'
(Other definitions for galahad that I've seen before include "Chivalrous knight" , "Round Table knight of immaculate purity" , "Noblest of King Arthur's knights" , "The most virtuous knight of the King Arthur's Round Table" , "noble man" .)