Main Entry: cantus fir·mus

Pronunciation: \-ˈfir-məs, -ˈfər-\

Function: noun

Etymology: Medieval Latin, literally, fixed song

Date: 1847

1 : the plainsong or simple Gregorian melody originally sung in unison and prescribed as to form and use by ecclesiastical tradition
2 : a melodic theme or subject; especially : one for contrapuntal treatment