Pentecost (7)
I believe the answer is:
whitsun
'pentecost' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for whitsun that I've seen before include "Holy Spirit festival" , "Period seven weeks after Easter" , "Wins hut on short Christian Sabbath" , "Feast" , "Pentecost season" .)