I think it is 'epidermis'.
Another word for Earth's outer surface is "crust."
Another word for the earth's surface is "ground" or "terrain".
its another word for outer.
Big dipper is an outer space word. Black hole is another outer space word that begins with the letter b.
The curved outer surface of a circle is the perimeter.
The outer surface of the bone is called the periosteum.
Tectonic plates
Tectonic plates.
Tectonic plates
Pinna is also known as the outer 'Ear'
tyre service
The word contamination comes to mind.