n. a type of medieval polyphony which builds upon an existing plainsong
The Century Dictionary and Cyclopedia
n. Same as organon.
n. In music: An organ.
n. Same as diaphony, 2.
Word Usage
"Nativitas gloriose virginis is a three-part organum, which is attributed to the medieval French composer Perotinus fl c.1200, who is also known as Pérotin."