1. A device that controls the flow of a gas or fluid through a pipe: A ventil can be a valve on a musical instrument, for example on a trumpet.

In organ-building, a ventil is a shutter in a wind-trunk which can admit wind in or cut off wind from two or more stops at once time.
2. An apparatus that allows fuel and air into the cylinder of an internal combustion engine, or one that makes it possible for combustion gases to exit.
3. In anatomy, one or more membranous partitions, flaps, or folds, which permit the passage of the contents of a vessel or cavity in one direction, but stop or retard the flow in the opposite direction: A ventil can also be described as the ileocolic (small intestine and large intestine valve), mitral (heart valve), of the semilunar (valves at the beginning of the artery of the heart).