des·cant • n. / ˈdesˌkant/ Mus. an independent treble melody usually sung or played above a basic melody. ∎ archaic or poetic/lit. a melodious song. ∎  a discourse on a theme or subject: his descant of deprivation.• v. / desˈkant/ [intr.] talk tediously or at length: I have descanted on this subject before.

descant. Like ‘faburden’ a puzzling term because at different periods used with different significances, chief of which are as follows: (1) A term, usually spelt discant, for a form of the 12th cent. part-writing known as organum. (2) A part extemporized by a singer to a non-extemporized part sung by another singer. (3) The art of composing or singing part-music. (4) The soprano part in choral music. (5) In modern hymn singing, a freely written or improvised soprano part added to a hymn tune while the tune itself is sung by the rest of the choir or by the congregation.

descant sb. XIV. orig. deschaunt — OF. deschant (mod. déchant) — medL. discantus part-song, refrain f. L. dis- asunder, apart + cantus song; see DIS-, CHANT. The present form is due to partial assim. to L.
So descant vb. XVI. prob. f. the sb.