opera house vs theater

opera house and theater both are nouns.

Word	Noun	Adjective	Verb	Adverb
opera house	Yes	No	No	No
theater	Yes	No	No	No

As nouns, theater is a hypernym of opera house; that is, theater is a word with a broader meaning than opera house:

opera house: a building where musical dramas are performed
theater: a building where theatrical performances or motion-picture shows can be presented

Other hypernyms of opera house include house, theatre.

opera house (noun)	theater (noun)
a building where musical dramas are performed	a building where theatrical performances or motion-picture shows can be presented
	the art of writing and producing plays
	a region in which active military operations are in progress