tube

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

(noun) electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope. Synonyms: vacuum tube, thermionic vacuum tube, thermionic tube, electron tube, thermionic valve.

(noun) a hollow cylindrical shape. Synonyms: pipe.

(noun) (anatomy) any hollow cylindrical body structure. Synonyms: tube-shaped structure.

(noun) an electric railway operating below the surface of the ground (usually in a city). Synonyms: metro, underground, subway system, subway. Example: "In paris the subway system is called the `metro' and in london it is called the `tube' or the `underground'."

(verb) provide with a tube or insert a tube into.

(verb) convey in a tube. Example: "Inside paris, they used to tube mail."

(verb) ride or float on an inflated tube. Example: "We tubed down the river on a hot summer day."

(verb) place or enclose in a tube.