What is the meaning of Arcus?

A white band of cholesterol that forms at the edge of the cornea

A low, horizontal cloud typically forming at the leading edge of thunderstorm outflow

An elastic band around the base of the arolium, a pad at the end of the leg of certain insects

An arc-shaped band of thickened sexine extending between two apertures on a pollen grain or spore

arc, arch

bow (arc-shaped weapon used for archery)

rainbow

Source: wiktionary.org