Cantus firmus
DEFINITION
The basis of polyphonic compositions of the Middle Ages and Renaissance. The tune of the cantus firmus was taken from Gregorian chant; it would move very slowly underneath more rapid vocal or instrumental lines above it.fixed melody. this usually describes a melody borrowed from another source and used as the basis of the work, with other melodies being set in counterpoint against it. this was very common during the 14th and 17-centuries