Scrap religious festival (4)
I believe the answer is:
whit
This clue could be a double definition.
'scrap' is the first definition.
(both can mean a tiny amount)
'religious festival' is the second definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
Can you help me to learn more?
(Other definitions for whit that I've seen before include "Pentecost (abbrev.)" , "Iota" , "Smallest imaginable particle" , "Festival week" , "A little" .)