a structure in a hollow organ (like the heart) with a flap to insure one-way flow of fluid through it
"The surgeon carefully repaired the damaged valve in his patient's heart to restore proper blood flow."
device in a brass wind instrument for varying the length of the air column to alter the pitch of a tone
"The trumpet player pressed down on the second valve to drop the note an entire step lower."
control consisting of a mechanical device for controlling the flow of a fluid
"The mechanic tightened the valve to stop the water from leaking out of the pipe."
the entire one-piece shell of a snail and certain other molluscs
"The ancient fossil revealed itself as a smooth, spiral valve preserved in the limestone rock."
one of the paired hinged shells of certain molluscs and of brachiopods
"The diver carefully examined the worn valve on the ancient clam shell before adding it to her collection."
A device that controls the flow of a gas or fluid through a pipe.
"The mechanic replaced the faulty valve to stop the oil from leaking out of the engine block."
In plain English: A valve is a device that controls the flow of liquids or gases by opening, closing, or restricting a passage.
"The mechanic replaced the faulty engine valve to fix the car's performance."
To control (flow) by means of a valve.
"She quickly turned the valve to stop the water from leaking out of the pipe."
In plain English: To valve something means to control or regulate its flow by opening or closing a passage.
"Please open the valve to let some air out before you tighten the tire."
Usage: Use this verb when describing the physical act of regulating fluid or gas flow through an opening, such as turning on water to fill a tank. It is distinct from nouns like tap or switch because it specifically implies mechanical restriction rather than simple connection or electrical control.
The word "valve" comes from the Latin valva, which originally meant a double door. It entered Middle English with this same meaning before evolving to refer to the mechanical device that controls fluid flow.