Definition
A mechanical valve or fitting used to control or shut off the flow of a fluid, such as fuel, oil, hydraulic fluid, or air, in an aircraft system. Operated by a handle, lever, or knob that opens, closes, or selects the path of the flow.
Plain English
A type of valve in an aircraft system that you turn or move to start, stop, or redirect the flow of a liquid or gas.
Context Anchor
Seen in aircraft manuals and checklists in terms such as fuel cock, drain cock, or shutoff cock.
Derivation
From Old English 'cocc,' originally referring to a spout or tap that controls flow, likely named for its resemblance to a rooster's head and beak when the handle was turned. The plumbing sense (a tap or valve) is centuries old and carries directly into mechanical and aviation usage.
Why Pilots Care
Provides a quick way to shut off fuel or oil flow during emergencies, maintenance, or before flight.
Analogy
A cock works like the small handle on a garden hose connection: turn it one way and flow is allowed, turn it the other way and flow stops.
Intuition Check
Do not read cock here as the everyday word for a bird or as part of cockpit. In aircraft system language, cock means a small flow-control valve or tap.
Example Sentence 1
The pilot closed the fuel cock to shut off the supply to the engine before securing the aircraft.
Example Sentence 2
Open the oil cock fully to ensure proper lubrication during the engine run-up.