To comment at length; discourse: "He used to descant critically on the dishes which had been at table"(James Boswell).
also dis·cant (dĭs'kānt', dĭ-skānt') Music
To sing or play a descant.
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 Indo-European roots.] des'cant'er n.
[n., adj. des-kant; v. des-kant, dis-] 
).