grand opera vs opera

grand opera and opera both are nouns.

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

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

grand opera: opera in which all the text is sung
opera: a drama set to music; consists of singing with orchestral accompaniment and an orchestral overture and interludes

grand opera (noun)	opera (noun)
opera in which all the text is sung	a building where musical dramas are performed
	a drama set to music; consists of singing with orchestral accompaniment and an orchestral overture and interludes