valve

(noun) a structure in a hollow organ (like the heart) with a flap to insure one-way flow of fluid through it.

(noun) device in a brass wind instrument for varying the length of the air column to alter the pitch of a tone.

(noun) control consisting of a mechanical device for controlling the flow of a fluid.

(noun) the entire one-piece shell of a snail and certain other molluscs.

(noun) one of the paired hinged shells of certain molluscs and of brachiopods.