any device that shuts off, starts, regulates, or controls the flow of a fluid
2. anatomy
a flaplike structure in a hollow organ, such as the heart, that controls the one-way passage of fluid through that organ
3. Also called: tube, vacuum tube
an evacuated electron tube containing a cathode, anode, and, usually, one or more additional control electrodes. When a positive potential is applied to the anode, electrons emitted from the cathode are attracted to the anode, constituting a flow of current which can be controlled by a voltage applied to the grid to produce amplification, oscillation, etc
See also diode (sense 2), triode (sense 1), tetrode, pentode
4. zoology
any of the separable pieces that make up the shell of a mollusc
5. music
a device on some brass instruments by which the effective length of the tube may be varied to enable a chromatic scale to be produced
6. botany
a.
any of the several parts that make up a dry dehiscent fruit, esp a capsule