Definition of "cantus firmus" [cantus firmus]

• A preexisting melody used as the basis of a polyphonic composition, especially in 14th- and 15th-century polyphony. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The folk-song of olden times, springing directly from and resembling the music of the Church, was often employed as motif or cantus firmus in masses and other liturgical compositions, a proceeding which would not be allowed now-a-days."