S: (n) metro, tube, underground, subway system, subway (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'"
Verb
S: (v) tube (provide with a tube or insert a tube into)
S: (v) tube (convey in a tube) "inside Paris, they used to tube mail"