opera house vs opera

opera house and opera both are nouns.

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

As nouns, opera house and opera are synonyms defined as:

opera house (noun)	opera (noun)
a building where musical dramas are performed	a building where musical dramas are performed
	a drama set to music; consists of singing with orchestral accompaniment and an orchestral overture and interludes