pastoral vs piece of music

pastoral and piece of music both are nouns.

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

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

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

pastoral (noun)	piece of music (noun)
a musical composition that evokes rural life	a musical work that has been created
a literary work idealizing the rural life (especially the life of shepherds)
a letter from a pastor to the congregation

pastoral (adjective)	piece of music (adjective)
of or relating to a pastor
relating to shepherds or herdsmen or devoted to raising sheep or cattle
(used with regard to idealized country life) idyllically rustic