tube

noun

1.
conduit consisting of a long hollow object (usually cylindrical) used to hold and conduct objects or liquids or gases
theet tubing
Derived from:
tube tubular
2.
electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope
electron tube thermionic tube thermionic vacuum tube thermionic valve vacuum tube
3.
a hollow cylindrical shape
sinweltling pipe
Derived from:
tube
4.
(anatomy) any hollow cylindrical body structure
tube-shaped structure
Derived from:
tubal tube
5.
an electric railway operating below the surface of the ground (usually in a city)
fastwain steadwain metro subway subway system underground