flatbread vs rusk

flatbread

noun
  • A thin, flat bread, often made from unleavened dough. 

rusk

noun
  • a rectangular, hard, dry biscuit 

  • a twice-baked bread, slices of bread baked until they are hard and crisp (also called a zwieback) 

  • a cereal binder used in meat product manufacture 

  • a weaning food for children 

How often have the words flatbread and rusk occurred in a corpus of books? (source: Google Ngram Viewer )