Definition
The structural components of an aircraft, typically including wheels, struts, tires, brakes, and shock-absorbing assemblies, that support the airplane on the ground and allow it to taxi, take off, and land. Landing gear may be fixed (permanently extended) or retractable (stowed in flight to reduce drag), and is configured as either tricycle (nosewheel forward) or conventional (tailwheel aft).
Plain English
The wheels and supporting parts the airplane sits, rolls, and lands on.
Context Anchor
You inspect the landing gear during preflight, especially the tires, brakes, and visible support parts, before the airplane moves.
Derivation
Landing means coming down onto a surface. Gear originally meant equipment or working parts used for a job. In aviation, landing gear means the equipment used for the job of supporting the aircraft when it is on or near the ground.
Why Pilots Care
A damaged or improperly configured landing gear can cause runway excursions, structural damage, or loss of control during critical ground phases.
Intuition Check
Do not read gear here as a toothed wheel in a machine or as loose equipment carried in the airplane. In this context, gear means the installed parts that support the airplane on the ground.
Example Sentence 1
During the preflight, the pilot inspected the landing gear for proper tire inflation, brake wear, and any signs of hydraulic leaks.
Example Sentence 2
After takeoff the pilot confirmed the landing gear had retracted and the gear-up lights were illuminated.