air cushion

1. Trapped air that supports a vehicle a short distance above the surface of land or water.
2. A device that uses trapped air to absorb the shock of motion, especially in vehicles. Also called air spring.

The noun has 3 meanings:

Meaning #1: the trapped air that supports a hovercraft a short distance above the water or ground

Meaning #2: a mechanical device using confined air to absorb the shock of motion
  Synonym: air spring

Meaning #3: a cushion usually made of rubber or plastic that can be inflated
  Synonym: inflatable cushion