[1] : The Collaborative International Dictionary of English v.0.48

zwieback \zwie"back`\ tsv=e"baumk`, 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.
   webster 1913 suppl.
see also:
twice 

[2] : WordNet (r) 2.0

zwieback
     n : slice of sweet raised bread baked again until it is brown
         and hard and crisp syn: rusk, brussels biscuit, twice-baked
         bread
see also:
rusk brussels biscuit twice-baked bread 

Zwieback >> Z Words
Zwieback, definition of term: Zwieback
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