Observance before Easter (4)
I believe the answer is:
lent
'observance before easter' 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 "Christian period of abstinence" , "Forty days of penance" , "days before Easter" , "Forty days of fasting" , "Period of penance" .)