Plain English Meaning
A part attached to the nosewheel that stops it from rapidly wobbling left and right when it is rolling on the ground.
Full Definition
A small hydraulic or friction device fitted to the nosewheel (or tailwheel) steering mechanism of an aircraft that absorbs and resists the rapid side-to-side oscillations the wheel can develop during taxi, takeoff, and landing rollout.
Context Anchor
Seen during preflight inspections, landing gear discussions, and maintenance write-ups for nosewheel or tailwheel aircraft.
Derivation
Shimmy is an old American English word for a shaking or wobbling movement (originally a kind of dance). Damper comes from damp, meaning to reduce or quiet something. So a shimmy damper is literally a device that quiets the wobble.
Why Pilots Care
Unchecked shimmy can damage the nose gear, cause loss of directional control, or lead to a runway excursion at high speed.
Analogy
It works somewhat like the part on a shopping cart wheel that would stop the wheel from fluttering back and forth at speed.
Intuition Check
A shimmy damper does not steer the airplane. It reduces unwanted wheel wobble so the wheel can track smoothly on the ground.
Example Sentence 1
During the walk-around, the pilot checked the shimmy damper on the nose gear for any sign of fluid leaking around the seals.
Example Sentence 2
After a hard landing the mechanic replaced the worn shimmy damper because the aircraft had developed a noticeable nosewheel shake on rollout.