zwieback

noun

1. (countable, uncountable)A form of rusk, usually sweetened bread enriched with eggs that is baked and then sliced and toasted until dry and crisp; considered easy to digest and therefore given to the ill and used as a teething food for toddlers.

   “Ogden Nash, Adventures Of Isabel She nibbled the zwieback that she always fed off, And when it was gone, she cut the giant's head off.”