Hymn trendy trio jazzed up after time (7)
I believe the answer is:
introit
'hymn' is the definition.
(thesaurus)
'trendy trio jazzed up after time' is the wordplay.
'trendy' becomes 'in'.
'jazzed up' indicates an anagram.
'after' is a charade indicator (letters next to each other).
'time' becomes 't'.
'trio' is an anagram of 'troi'.
'in'+'troi'+'t'='INTROIT'
(Other definitions for introit that I've seen before include "Introductory anthem" , "Pre-Eucharist prayer" , "Rot in it for a church entry hymn" , "Short prayer" , "chant" .)