tube

A hollow cylindrical shape.

(anatomy) 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”