program music vs opus

program music and opus both are nouns.

Word	Noun	Adjective	Verb	Adverb
program music	Yes	No	No	No
opus	Yes	No	No	No

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

program music: musical compositions intended to evoke images or remind the listener of events
opus: a musical work that has been created

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

program music (noun)	opus (noun)
musical compositions intended to evoke images or remind the listener of events	a musical work that has been created