Akademik

Gregorian chant
n. plainsong ritual music, named after Pope Gregory I.

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noun, pl ⋯ chants [count, noncount]
: a type of religious music from the Middle Ages that is sung without instruments

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Greˌgorian ˈchant noun uncountable, countable
a type of church music for voices alone, used since the Middle Ages
 
Word Origin:
[Gregorian chant] mid 18th cent.: named after St Gregory the Great (in Latin Gregorius), who is said to have standardized it.

Useful english dictionary. 2012.