Definition of "a cappella"

(music) A vocal performance with no instrumental accompaniment.  examples

(music) In a manner of a choir with no instrumental accompaniment; literally, "in the style of the (Sistine) Chapel (in Rome)", such as a musical Mass done a cappella.  examples

(obsolete, music) In alla breve time.

(music) Singing solely or mainly without instrumental accompaniment.  examples

(music, US) Related to a form of purely vocal music mostly associated with American college performance groups.  quotations  examples

(obsolete, music) alla breve.