silk hat vs opera hat

silk hat and opera hat both are nouns.

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

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

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

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

silk hat (noun)	opera 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