idyll vs opus

idyll and opus both are nouns.

Word	Noun	Adjective	Verb	Adverb
idyll	Yes	No	No	No
opus	Yes	No	No	No

As nouns, opus is a hypernym of idyll; that is, opus is a word with a broader meaning than idyll:

Other hypernyms of idyll include composition, musical composition, piece, piece of music.

idyll (noun)	opus (noun)
a short poem descriptive of rural or pastoral life	a musical work that has been created
a musical composition that evokes rural life
an episode of such pastoral or romantic charm as to qualify as the subject of a poetic idyll