cantus firmus
[ kan-tuh s fur-muh s ]
/ ˈkæn təs ˈfɜr məs /
noun
the ancient traditional unisonal plainchant of the Christian Church, having its form set and its use prescribed by ecclesiastical tradition.
Music.
a fixed melody to which other voices are added, typically in polyphonic treatment.
Origin of cantus firmus
1840–50; < Medieval Latin: literally, firm song