Hymn popular trio played with tenor (7)
I believe the answer is:
introit
'hymn' is the definition.
(thesaurus)
'popular trio played with tenor' is the wordplay.
'popular' becomes 'in'.
'played with' is an anagram indicator.
'tenor' becomes 't'.
'trio' mixed up with 't' can make 'troit'.
'in'+'troit'='INTROIT'
(Other definitions for introit that I've seen before include "Church psalm" , "Something musical" , "Rot in it for a church entry hymn" , "Short prayer" , "Opening hymn" .)