The term CRISP BISCUIT can be broken down into two crossword solutions: RUSK (4 letters) and WAFER (5 letters). A RUSK is a type of biscuit or cookie that is made from twice-baked bread. It is usually hard and dry, and is often served with tea or coffee. A WAFER is a thin, crisp cookie made from flour, sugar, and other ingredients. It is usually served as a dessert or snack. Both rusks and wafers are considered to be types of crisp biscuits.