Captain Caper starting the French nonmetrical hymn (8)
I believe the answer is:
canticle
'hymn' is the definition.
(I know that canticle is a type of hymn)
'captain caper starting the french nonmetrical' is the wordplay.
I cannot really see how this works, but
'caper' could be 'antic' (synonyms) and 'antic' is found within the answer.
'the french' could be 'le' ('the' in French) and 'le' is located in the answer.
A single letter 'c' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for canticle that I've seen before include "is heard in church" , "eg Magnificat" , "Bible-derived song or prayer" , "A religious song" , "Church hymn or chant" .)