Symphony (8)
(Other definitions for sinfonia that I've seen before include "Without limit" , "Orchestral piece" , "Small orchestra" , "Composition" , "Symphonic music - as if in no (anag)" .)
'symphony' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for orchestra that I've seen before include "Brass, woodwind, strings and percussion" , "those who provide the music" , "Company of musicians" , "Musicians, maybe in theatre" , "Big group of musicians playing various instruments" .)