Definition
A rapid, side-to-side oscillation of a nose or tail wheel, usually occurring during takeoff or landing roll, caused by wear, looseness, or imbalance in the wheel assembly, strut, or steering linkage.
Plain English
A fast wobble or shaking of the nose or tail wheel as the aircraft rolls along the ground.
Context Anchor
Seen in landing gear maintenance and felt during taxi, takeoff roll, or landing rollout when a wheel vibrates or wobbles.
Derivation
From the 1920s American slang 'shimmy,' a shaking dance, itself from 'chemise' (a loose shirt that shook with the dancer). The word was applied to wheels that wobble in the same rapid, side-to-side way.
Why Pilots Care
Unchecked shimmy can cause loss of directional control or damage to the landing gear and steering components.
Analogy
Like the wobble of a loose supermarket trolley wheel — except at much higher speed and with much more at stake.
Intuition Check
Shimmy does not mean any small vibration. In aircraft maintenance, it means a rapid side-to-side wobble of a wheel or landing gear assembly that needs attention.
Example Sentence 1
On the landing rollout, the pilot felt a shimmy in the nose wheel and reported it to maintenance.
Example Sentence 2
Replacing the worn tire eliminated the shimmy that appeared on every landing rollout.