Definition
Rotating in the direction opposite to the movement of the hands of a clock when viewed from a stated reference point. In aviation, the viewing reference must be specified (for example, viewed from behind the airplane looking forward, or viewed from above), because the same rotation appears clockwise from the opposite side.
Plain English
Turning the opposite way that clock hands move, when you are looking at it from a stated direction.
Context Anchor
Seen in airplane descriptions when a part, control, or airflow pattern is described as turning or moving in a specific direction.
Derivation
From 'counter' (against, opposite) and 'clockwise' (in the direction a clock's hands move). The word literally means 'against the clock's direction.'
Why Pilots Care
Ensures pilots and mechanics interpret rotation directions correctly during preflight inspections and engine operation.
Intuition Check
Do not assume counterclockwise is the same from every side. If you view the same rotating part from the opposite side, the apparent direction can reverse.
Example Sentence 1
Viewed from the cockpit looking forward, the propeller on most American-built single-engine airplanes rotates clockwise, not counterclockwise.
Example Sentence 2
Confirm the rotor spins counterclockwise before completing the gyro instrument check.