Something for Sunday before Easter includes second hymn (5)
I believe the answer is:
psalm
'hymn' is the definition.
(type of hymn)
'something for sunday before easter includes second' is the wordplay.
'something for sunday before easter' becomes 'palm' (as in Palm Sunday).
'includes' indicates putting letters inside.
'second' becomes 's' (common abbreviation).
'palm' going around 's' is 'PSALM'.
(Other definitions for psalm that I've seen before include "Sacred poem attributed to David" , "Sacred song of praise" , "Sacred Biblical song" , "Song of David" , "Palms (anag.)" .)