sostenutoPronunciation: /ˌsɒstəˈnuːtəʊ/ MusicDefinition of sostenuto adjective (of a passage of music) to be played in a sustained or prolonged manner. noun (plural sostenutos) a passage to be played in a sustained or prolonged manner. [mass noun] the performance of a passage in a sustained or prolonged manner. Origin:Italian, 'sustained'sostenuto in other Oxford dictionaries Definition of sostenuto in the US English dictionary