I. adjective Etymology: Italian, obligatory, from past participle of obbligare to oblige, from Latin obligare — more at oblige not to be omitted; obligatory — used as a direction in music; compare ad libitum II. noun (plural -tos; also obbligati) 1. an elaborate especially melodic part accompanying a solo or principal melody and usually played by a single instrument Example: a song with violin obbligato 2. accompaniment 2b; especially an attendant background sound