plainsong
/ˈpleɪnsɒŋ/noun
mass noun
- unaccompanied church music sung in unison in medieval modes and in free rhythm corresponding to the accentuation of the words, which are taken from the liturgy素歌（根据从圣餐仪式上摘选的话语的重音以中世纪模式和自由节奏吟唱的无伴奏教堂音乐）。比较GREGORIAN CHANT.
词源
late Middle English: translating Latin cantus planus.