musical composition vs piece of music

musical composition and piece of music both are nouns.

Word	Noun	Adjective	Verb	Adverb
musical composition	Yes	No	No	No
piece of music	Yes	No	No	No

As nouns, musical composition and piece of music are synonyms defined as:

musical composition and piece of music: a musical work that has been created

Other synonyms of musical composition include composition, opus, piece.

musical composition (noun)	piece of music (noun)
a musical work that has been created	a musical work that has been created