ob·bli·ga·to also ob·li·ga·to 
(ŏb′lĭ-gätō)Music
(ŏb′lĭ-gätō)Music adj.
Not to be left out; indispensable. Used of an accompaniment that is an integral part of a piece.
n. pl. ob·bli·ga·tos or ob·bli·ga·ti (-tē) also ob·li·ga·tos or ob·li·ga·ti
An obbligato accompaniment.
[Italian, past participle of obbligare, to obligate, from Latin obligāre, to oblige; see OBLIGE.]