Outer (adjective)

1. Situated on the outside; external.
2. Further from the center or the middle.
3. On or towards the outside edge of something.

Origin:

Old english ūtan "outside".

Examples:

1. The outer surface of the planet.
2. The outer layer of skin.
3. The outer rim of the wheel.
4. The outer suburbs of the city.
5. The outer limits of the universe.