Novel carol initially heard sung by choir (6)
I believe the answer is:
choral
'sung by choir' is the definition.
(I've seen this before)
'novel carol initially heard' is the wordplay.
'novel' indicates an anagram.
'initially' suggests taking the first letters.
The first letter of 'heard' is 'h'.
'carol'+'h'='carolh'
'carolh' anagrammed gives 'CHORAL'.
(Other definitions for choral that I've seen before include "To do with group of singers, often in church" , "Sung by a band of singers" , "Involving many singers" , "Sung by group of singers" , "Sung psalm" .)