rusk

noun4

1. •
   A rectangular, hard, dry biscuit.

   • […] he brought a large basket of rusk or biscuit, and three jars of fresh water, into the boat. — 1719
2. •
   A twice-baked bread, slices of bread baked until they are hard and crisp; zwieback.
3. •
   A weaning food for children.
4. •
   A cereal binder used in meat product manufacture.