Brussels biscuit vs zwieback

Brussels biscuit and zwieback both are nouns.

Word	Noun	Adjective	Verb	Adverb
Brussels biscuit	Yes	No	No	No
zwieback	Yes	No	No	No

As nouns, Brussels biscuit and zwieback are synonyms defined as:

Brussels biscuit and zwieback: slice of sweet raised bread baked again until it is brown and hard and crisp

Other synonyms of Brussels biscuit include rusk, twice-baked bread.

Brussels biscuit (noun)	zwieback (noun)
slice of sweet raised bread baked again until it is brown and hard and crisp	slice of sweet raised bread baked again until it is brown and hard and crisp