Some French jargon that is sung (7)
I believe the answer is:
descant
'is sung' is the definition.
I can't judge whether this defines the answer.
'some french jargon' is the wordplay.
'some french' becomes 'des' ('some' in French).
'jargon' becomes 'cant' (synonyms).
'des'+'cant'='DESCANT'
'that' acts as a link.
Can you help me to learn more?
(Other definitions for descant that I've seen before include "Sung variation" , "Independent melody sung above a basic melody" , "Accompaniment added above a basic melody" , "Upper melody" , "Ornamental melody added above a theme" .)