Noun

1. Conduit consisting of a long hollow object (usually cylindrical) used to hold and conduct objects or liquids or gases
2. Electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope
3. A hollow cylindrical shape
4. (anatomy) any hollow cylindrical body structure
5. An electric railway operating below the surface of the ground (usually in a city)

Verb

1. Provide with a tube or insert a tube into
2. Convey in a tube
3. Ride or float on an inflated tube
4. Place or enclose in a tube