Ash Wednesday starts it (4)
I believe the answer is:
lent
'ash wednesday starts it' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lent that I've seen before include "Gave the use of for a time" , "From Ash Wednesday to Holy Saturday" , "Period of penance" , "Pre-Easter period" , "Gave for a limited period" .)