obbligato
Noun
Meaning
a part of the score that must be performed without change or omission
a persistent but subordinate motif
Source: WordNetSynonyms
obligato
apply
corresponding
joint
copy
fellow
adopt
comparable
harmony
backing
companion
accompanying
accompany
accompaniment
attendant
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Antonyms
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Examples
Composers such as Boccherini would publish sonatas for piano and obbligato instrument with an optional third movement—–in Boccherini's case, 28 cello sonatas.
Some of his chamber music involves trombones, as do many of his operas, used as an obbligato instrument.