Discant

A descant, discant, or discantus is any of several different things in music, depending on the period in question; etymologically, the word means a voice (cantus) above or removed from others. The Harvard Dictionary of Music states: Anglicized form of L. discantus and a variant of discant. Throughout the Middle Ages the term was used indiscriminately with other terms, such as descant. In the 17th century it took on special connotations in instrumental practice.

A descant is a form of medieval music in which one singer sang a fixed melody, and others accompanied with improvisations. The word in this sense comes from the term discantus supra librum (descant "above the book"), and is a form of Gregorian chant in which only the melody is notated but an improvised polyphony is understood. The discantus supra librum had specific rules governing the improvisation of the additional voices.