What is the meaning of tube?

noun

• Conduit consisting of a long hollow object (usually cylindrical) used to hold and conduct objects or liquids or gases.
  • synonyms: tubing
• 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
• A hollow cylindrical shape.
  • synonyms: pipe
• Anatomy) any hollow cylindrical body structure.
  • synonyms: tube-shaped structure
• An electric railway operating below the surface of the ground (usually in a city. )
  • usage: "in Paris the subway system is called the `metro' and in London it is called the `tube' or the `underground'"
  • synonyms: metro, underground, subway system, subway

verb

• Provide with a tube or insert a tube into.
• Convey in a tube.
  • usage: "inside Paris, they used to tube mail"
• Ride or float on an inflated tube.
  • usage: "We tubed down the river on a hot summer day"
• Place or enclose in a tube. .