pastiche vs piece of music

pastiche and piece of music both are nouns.

Word	Noun	Adjective	Verb	Adverb
pastiche	Yes	No	No	No
piece of music	Yes	No	No	No

As nouns, piece of music is a hypernym of pastiche; that is, piece of music is a word with a broader meaning than pastiche:

pastiche: a musical composition consisting of a series of songs or other musical pieces from various sources
piece of music: a musical work that has been created

Other hypernyms of pastiche include composition, musical composition, opus, piece.

pastiche (noun)	piece of music (noun)
a work of art that imitates the style of some previous work	a musical work that has been created
a musical composition consisting of a series of songs or other musical pieces from various sources