noun conduit consisting of a long hollow object (usually cylindrical) used to hold and conduct objects or liquids or gases
Synonymstubing
noun electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope
noun a hollow cylindrical shape
Synonymspipe
noun (anatomy) any hollow cylindrical body structure
Synonymstube-shaped structure
noun an electric railway operating below the surface of the ground (usually in a city)
Source: WordNet 3.1, Princeton University