flue (n.)

"smoke channel in a chimney," 1580s, of uncertain origin, perhaps related to Middle English flue, flewe "mouthpiece of a hunting horn" (early 15c.), which is perhaps from Old French fluie "stream;" or the modern word is perhaps from Middle Dutch vluwe, from Germanic *flowan "to flow" (see flow (v.)). Originally a small chimney in a furnace connected to the main chimney.