1. (n.) A pipe in a chimney or organ for directing a current of air or gasses; an air passage.

2. (n.) A compartment or division of a chimney for conveying flame and smoke to the outer air.

3. (n.) A passage way for conducting a current of fresh, foul, or heated air from one place to another.

4. (n.) A pipe or passage for conveying flame and hot gases through surrounding water in a boiler; -- distinguished from a tube which holds water and is surrounded by fire. Small flues are called fire tubes or simply tubes.

5. (n.) Light down, such as rises from cotton, fur, etc.; very fine lint or hair.