Calm relative with good prayers (8)
I believe the answer is:
evensong
'prayers' is the definition.
(thesaurus)
'calm relative with good' is the wordplay.
'calm' becomes 'even' (I've seen this before).
'relative' becomes 'son' (son is a kind of relative).
'with' says to put letters next to each other.
'good' becomes 'g' (abbreviation).
'even'+'son'+'g'='EVENSONG'
(Other definitions for evensong that I've seen before include "Church service late in the day" , "... Prayers" , "Service of evening prayer in Church of England" , "6 [SERVICE] ?" , "Late afternoon church service" .)