Tube (structure) definition

(1) 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'"

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

(3) Electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope

(4) (anatomy) any hollow cylindrical body structure

(5) A hollow cylindrical shape

(6) Place or enclose in a tube

(7) Ride or float on an inflated tube

"We tubed down the river on a hot summer day"

(8) Convey in a tube

"Inside Paris, they used to tube mail"

(9) Provide with a tube or insert a tube into