Gregorian chants (Topical Term)

New Grove dict. of mus.: Gregorian and Old Roman chant (Old Roman chant is a liturgical repertory of melodies which survives in certain MSS dating from between the 11th and 13 centuries, but can be traced back at least as far as the 8th century. The relationship between this repertory and the Gregorian repertory is highly complex. Plainchant (plainsong), the official monophonic unison chant (originally unaccompanied) of the Christian liturgies. The term, though general, is used to refer particularly to the chant repertories with Latin texts--i.e. those of the five major Western Christian liturgies--or in a more restricted sense of the repertory of Franco-Roman chant (Gregorian chant).)

New Harvard dict. of mus.: Gregorian chant (the plainsong or liturgical chant of the Roman Catholic Church. Plainsong: monophonic Christian liturgical chant in free rhythm, as distinct from measured music; also plainchant)