Plainchant

noun

1. A form of monophonic chant in unison using the Gregorian scale, sung in various Christian churches.
2. A cantus firmus or theme chosen for contrapuntal treatment; so called because often an actual fragment of plain-song.
3. The simple notes of an air, without ornament or variation.
4. (by extension) A plain unvarnished statement, without exaggeration.