larghetto vs piece of music

larghetto and piece of music both are nouns.

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

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

larghetto: (music) a composition or passage played in a slow tempo slightly faster than largo but slower than adagio
piece of music: a musical work that has been created

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

larghetto (noun)	piece of music (noun)
(music) a composition or passage played in a slow tempo slightly faster than largo but slower than adagio	a musical work that has been created

larghetto (adjective)	piece of music (adjective)
(of tempo) less slow and broad than largo