The term AIR PIPE can be broken down into two crossword solutions: DUCT (4 letters) and AIRPASSAGE (10 letters). DUCT is a tube or conduit made of metal, plastic, or other material, used to convey air, water, or other fluid. An AIRPASSAGE is a passage through which air passes, such as a pipe, DUCT, or channel. Both terms are commonly used in the construction industry to refer to systems that allow air to flow through a building.