n.1. a. A hollow cylinder, especially one that conveys a fluid or functions as a passage.
b. An organic structure having the shape or function of a tube; a duct: a bronchial tube.
2. A small flexible cylindrical container sealed at one end and having a screw cap at the other, for pigments, toothpaste, or other pastelike substances.
3. Music The cylindrical part of a wind instrument.
4. Electronics a. An electron tube.
b. A vacuum tube.
5. Botany The lower, cylindrical part of a gamopetalous corolla or a gamosepalous calyx.
6. a. A tunnel.
b. An underground railroad system, especially the one in London, England.
7. The elongated space inside a wave when it is breaking.
8. a. An inner tube.
b. An inflatable tube or cushion made of rubber or plastic and used for recreational riding, as behind a motor boat or down a snow-covered slope.
9. Informal a. Television: What's on the tube?
b. A television set.
10. tubes Informal The fallopian tubes.