The term 'Flue Coat' is a type of protective clothing worn by workers in the chimney sweeping industry. The crossword solution for this term is 'SOOT', which is a black or dark-colored powdery or flaky substance made up of tiny particles of carbon that is produced by the burning of organic matter. SOOT is often found on the walls and surfaces of chimneys, and is one of the main components of flue coat.