a cappella
/ˌɑːkəˈpelə/adjective & adverb
- (with reference to choral music) sung without instrumental accompaniment（合唱乐）无器乐伴奏的（地）：
as adj. an a cappella Mass清唱弥撒曲
as adv. the consorts usually perform a cappella.合唱队通常表演无伴奏清唱。
词源
Italian, literally 'in chapel style'.