any of various usually cylindrical structures or devices: such as a hollow elongated cylinder - a soft tubular container whose contents (such as toothpaste) can be removed by squeezing - TUNNEL - SUBWAY sense b - the basically cylindrical section between the mouthpiece and bell that is the fundamental part of a wind instrument. a slender channel (such as a fallopian tube or a pollen tube) within a plant or animal body: DUCT. the narrow basal portion of a corolla with united petals or a calyx with united sepals. INNER TUBE. ELECTRON TUBE. CATHODE-RAY TUBE. TELEVISION. an article of clothing shaped like a tube.