from the GNU version of the Collaborative International Dictionary of English
- n. a valve in the form of a circular disk, which covers a hole in its seat, and opens by moving bodily away from the seat while remaining parallel with it, -- used in steam engines, pumps, safety valves, etc. Its edge is often beveled, and fits in a conical recess in the seat when the valve is closed. See the valves shown in Illusts. of Plunger pump, and Safety valve, under Plunger, and Safety.
Sorry, no etymologies found.