a cappella a cappella /ə ˌkɑːˈpɛlə/

adjective

1. Sung without instrumental accompaniment  ( a capella , a cappella )
   sung without instrumental accompaniment
    They sang an a cappella Mass
   they sang an a cappella Mass
   

adverb

1. Without musical accompaniment  ( a capella , a cappella )
   without musical accompaniment
    They performed a cappella
   they performed a cappella