opera hat vs top hat

opera hat and top hat both are nouns.

Word	Noun	Adjective	Verb	Adverb
opera hat	Yes	No	No	No
top hat	Yes	No	No	No

As nouns, opera hat and top hat are synonyms defined as:

opera hat and top hat: a man's hat with a tall crown; usually covered with silk or with beaver fur

Other synonyms of opera hat include beaver, dress hat, high hat, silk hat, stovepipe, topper.

opera hat (noun)	top hat (noun)
a man's hat with a tall crown; usually covered with silk or with beaver fur	a man's hat with a tall crown; usually covered with silk or with beaver fur