obbligato
noun /ˌɒblɪˈɡɑːtəʊ/
  /ˌɑːblɪˈɡɑːtəʊ/
(North American English also obligato)
 (plural obbligatos, North American English also obligatos)
 (from Italian, music- an important part for an instrument in a piece of music which cannot be left out必需声部;助奏 词源Italian, literally ‘obligatory’, from Latin obligatus, past participle of obligare, from ob- ‘towards’ + ligare ‘to bind’.