Literally, "twice-baked"

• Rusk
• Rebaked bread slice
• Slice of sweet raised bread baked again until it is brown and hard and crisp
• Dry, crisp bread
• Hard bread
• Twice-baked bread

Wikipedia Word definitions in Wikipedia
Zwieback is a form of rusk eaten in Scandinavia, Germany, Austria, France, Switzerland, Italy, Slovenia, and Greece. It is a type of crisp, sweetened bread , made with eggs and baked twice. It originated in East Prussia . The Mennonites brought Zwieback ...

Wiktionary Word definitions in Wiktionary
n. 1 a usually sweetened bread enriched with eggs that is baked and then sliced and toasted until dry and crisp 2 a teething food for toddler children

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Zwieback \Zwie"back`\ (tsv[=e]"b[aum]k`), n. [G., fr. zwie- two, twice (see Twice ) + backen to bake.] A kind of biscuit or rusk first baked in a loaf and afterwards cut and toasted.

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1894, from German Zweiback "biscuit," literally "twice-baked," from zwei "two, twice" + backen "to bake;" loan-translation of Italian biscotto (see biscuit ).