Noun

1. A structure in a hollow organ (like the heart) with a flap to insure one-way flow of fluid through it
2. Device in a brass wind instrument for varying the length of the air column to alter the pitch of a tone
3. Control consisting of a mechanical device for controlling the flow of a fluid
4. The entire one-piece shell of a snail and certain other molluscs
5. One of the paired hinged shells of certain molluscs and of brachiopods