The term 'OIL UNIT' can be solved by the crossword solution 'BARREL', which is a six-letter word. A BARREL is a unit of measurement used to measure oil and other liquids. It is equal to 42 gallons in the United States and 36 imperial gallons in the United Kingdom. The term is also used to refer to a large cylindrical container made of wood or metal, which is used to store and transport liquids such as oil.