descant: [14] Etymologically, descant is a parallel formation to English part song. English acquired it via Old French deschant from medieval Latin discantus ‘refrain’, a compound noun formed from the prefix dis- ‘apart’ and cantus ‘song’. The notion originally underlying it is of a separate vocal line ‘apart’ from the main musical theme. The Middle English form of the word was deschaunt; descant represents a partial 16th-century reversion to Latin discantus. => canto, chant
late 14c., from Old North French descant (Old French deschant), from Medieval Latin discantus "refrain, part-song," from Latin dis- "asunder, apart" (see dis-) + cantus "song" (see chant). Spelling was partly Latinized 16c. Originally "counterpoint."