descant (n.)
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."
descant (v.)
mid-15c.; see descant (n.). Sense of "to comment at length" is first attested 1640s.