Meaning of cantus firmus

can•tus fir•mus

Pronunciation: (kan'tus fûr'mus), [key]
  1. the ancient traditional unisonal plainchant of the Christian Church, having its form set and its use prescribed by ecclesiastical tradition.
  2. a fixed melody to which other voices are added, typically in polyphonic treatment.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.