des·cant 
(dĕskănt′)
(dĕskănt′)n.
1. also dis·cant (dĭs-) Music
a. An ornamental melody or counterpoint sung or played above a theme.
b. The highest part sung in part music.
2. A discussion or discourse on a theme.
intr.v. (dĕskănt′, dĕ-skănt) des·cant·ed, des·cant·ing, des·cants
1. To comment at length; discourse: "He used to descant critically on the dishes which had been at table" (James Boswell).
2. also dis·cant (dĭskănt′, dĭ-skănt) Music
a. To sing or play a descant.
b. To sing melodiously.
[Middle English, from Anglo-Norman descaunt, from Medieval Latin discantus, a refrain : Latin dis-, dis- + Latin cantus, song (from past participle of canere, to sing; see kan- in the Appendix of Indo-European roots).]
descant′er n.