Definition
Adverse yaw occurring to the left, typically when the pilot rolls into a right turn. The down-aileron on the left wing increases lift and drag on that wing, pulling the nose to the left -- opposite the direction of the intended right roll. In maneuvers such as the Lazy Eight, left adverse yaw must be countered with right rudder to keep the nose tracking correctly through the turn.
Plain English
When you roll the airplane to the right, the nose tries to swing the wrong way -- to the left -- because the left wing creates extra drag as its aileron goes down. You use right rudder to stop that and keep the nose going where you want.
Context Anchor
Encountered during lazy eights and other maneuvering practice, where the pilot must keep the airplane turning smoothly while pitch and bank are changing.
Derivation
Adverse' comes from Latin 'adversus,' meaning 'turned against' or 'opposite.' 'Yaw' is the side-to-side movement of the nose around the vertical axis. So 'adverse yaw' literally means the nose yawing in the opposite direction from what you'd expect during a roll. 'Left' simply specifies which way that unwanted yaw is happening.
Why Pilots Care
Uncorrected adverse yaw produces uncoordinated flight, which feels sloppy, wastes performance, and at low speeds with steep bank can contribute to a stall/spin. Recognizing left adverse yaw and applying right rudder in time is a basic stick-and-rudder skill examiners look for.
Grounding Statement
When the pilot rolls the airplane and one wing makes more drag than the other, that extra drag can pull the nose left.
Intuition Check
Do not read left adverse yaw as the left wing dropping. It means the nose is swinging left; adverse means that swing is working against the desired smooth, coordinated motion.
Example Sentence 1
As the student rolled into the right-hand climbing turn of the Lazy Eight, left adverse yaw pulled the nose off heading, so the instructor reminded her to add a touch of right rudder.
Example Sentence 2
Rudder applied with the aileron prevented left adverse yaw and kept the maneuver coordinated.