plainsong

/P L EY1 N S AO0 NG/
noun
  1. 1

    A form of monophonic chant in unison using the Gregorian scale, sung in various Christian churches.

  2. 2

    A cantus firmus or theme chosen for contrapuntal treatment; so called because often an actual fragment of plain-song.

  3. 3

    The simple notes of an air, without ornament or variation.

  4. 4

    (by extension) A plain unvarnished statement, without exaggeration.

Synonyms

Source: https://en.wiktionary.org/wiki/plainsong