A long, hollow cylinder of metal, plastic, glass, etc., for holding or transporting something, chiefly liquids or gases. A thing in the form of or resembling a tube, in particular. The subway system in London. A sealed container, typically of glass and either evacuated or filled with gas, containing two electrodes between which an electric current can be made to flow. Provide with a tube or tubes. Fit (a person or animal) with a tube to assist breathing, especially after a laryngotomy.