The term 'FORT KNOX PIECE' can be solved by the crossword solution 'INGOT', which is a five-letter word. An INGOT is a block of metal that has been cast into a specific shape, usually a bar or block, for storage and transportation. Ingots are often made of precious metals such as gold, silver, and platinum, and are used in the production of coins, jewelry, and other items. The term 'FORT KNOX PIECE' is often used to refer to a valuable INGOT, particularly one made of gold or silver.