/ vælv; NAmE / noun
1.
a device for controlling the flow of a liquid or gas, letting it move in one direction only
—picture at bicycle
2.
a structure in the heart or in a vein that lets blood flow in one direction only
3.
a device in some brass musical instruments for changing the note
—picture at trumpet
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WORD ORIGIN
late Middle English (denoting a leaf of a folding or double door): from Latin valva .