The prefix des-, meaning "two" or "apart", indicates that the descant is a "second song" apart from the main melody. In popular songs a descant will often be sung at the very end to produce a thrilling climax.
Verb an English professor who loves to descant on his beloved Shakespeare the world-famous soprano descanted above the melody line
Recent Examples on the Web
Noun
The Hynde storyline, which includes her messing around with songs on an acoustic guitar, runs as a kind of descant against the personal and professional noise of the Pistols. Robert Lloyd, Los Angeles Times, 31 May 2022 This is a dark and defensive descant to a more substantial and necessary conversation about whiteness in America. Philip Kennicott, Washington Post, 3 July 2019
Word History
Etymology
Noun
Middle English dyscant, from Anglo-French & Medieval Latin; Anglo-French descaunt, from Medieval Latin discantus, from Latin dis- + cantus song — more at chant