Fineness measure is a term used to describe the measurement of the purity of a material. The two crossword solutions for this term are Karat (5 letters) and DENIER (6 letters). Karat is a unit of measurement used to determine the purity of gold, with 24 karat being the purest form. DENIER is a unit of measurement used to determine the fineness of a fiber, such as silk or nylon, with a higher DENIER indicating a thicker fiber.