The term 'FORT KNOX UNIT' is a combination of two crossword solutions, 'INGOT' and 'KARAT'. An INGOT is a block or bar of metal that has been cast into a specific shape for storage and transportation. It is often used as a raw material for further processing. A karat is a unit of measurement used to indicate the purity of gold and other precious metals. It is equal to 1/24th of the total weight of the metal. Together, these two terms refer to a unit of gold or other precious metal stored in Fort Knox, a United States Army post in Kentucky.