tube

a hollow cylindrical shape

any hollow cylindrical body structure

an electric railway operating below the surface of the ground (usually in a city)

“in Paris the subway system is called the `metro' and in London it is called the `tube' or the `underground'”

conduit consisting of a long hollow object (usually cylindrical) used to hold and conduct objects or liquids or gases

electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope

convey in a tube

“inside Paris, they used to tube mail”

place or enclose in a tube

provide with a tube or insert a tube into

ride or float on an inflated tube

“We tubed down the river on a hot summer day”