descant

n. [ OF. descant, deschant, F. déchant, discant, LL. discantus, fr. L. dis + cantus singing, melody, fr. canere to sing. See Chant, and cf. Descant, v. i., Discant. ] 1. (Mus.) (a) Originally, a double song; a melody or counterpoint sung above the plain song of the tenor; a variation of an air; a variation by ornament of the main subject or plain song. (b) The upper voice in part music. (c) The canto, cantus, or soprano voice; the treble. Grove. [ 1913 Webster ]

Twenty doctors expound one text twenty ways, as children make descant upon plain song. Tyndale. [ 1913 Webster ]

She [ the nightingale ] all night long her amorous descant sung. Milton. [ 1913 Webster ]

☞ The term has also been used synonymously with counterpoint, or polyphony, which developed out of the French déchant, of the 12th century. [ 1913 Webster ]

2. A discourse formed on its theme, like variations on a musical air; a comment or comments. [ 1913 Webster ]

Upon that simplest of themes how magnificent a descant! De Quincey. [ 1913 Webster ]