organum

or·ga·num ¹  (ôrg-nm)

n. pl. or·ga·na (-n) or or·ga·nums

Any of several types of medieval vocal polyphony, usually based on Gregorian chant.

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[Medieval Latin, from Late Latin, church organ, from Latin, instrument; see organ.]

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or·ga·num ²  (ôrg-nm)

n. pl. or·ga·nums

Variant of organon.

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organum [ˈɔːgənəm]

n pl -na [-nə], -nums

1. (Music, other) a form of polyphonic music originating in the ninth century, consisting of a plainsong melody with parts added at the fourth and fifth

2. (Philosophy / Logic) a variant of organon

[via Latin from Greek; see organ]