capriccio vs piece of music

capriccio and piece of music both are nouns.

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

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

capriccio: an instrumental composition that doesn't adhere to rules for any specific musical form and is played with improvisation
piece of music: a musical work that has been created

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

capriccio (noun)	piece of music (noun)
an instrumental composition that doesn't adhere to rules for any specific musical form and is played with improvisation	a musical work that has been created