[kan-tuh
s fur-muhs] 
| 1. | the ancient traditional unisonal plainchant of the Christian Church, having its form set and its use prescribed by ecclesiastical tradition. |
| 2. | Music. a fixed melody to which other voices are added, typically in polyphonic treatment. |
| can·tus fir·mus (kān'təs fîr'məs, fûr'-) n. A preexisting melody used as the basis of a polyphonic composition, especially in 14th- and 15th-century polyphony. [Medieval Latin : Latin cantus, song + Latin firmus, fixed.] |