arcus

noun4

1. •
   A white band of cholesterol that forms at the edge of the cornea
2. •
   A low, horizontal cloud typically forming at the leading edge of thunderstorm outflow
3. •
   An elastic band around the base of the arolium, a pad at the end of the leg of certain insects
4. •
   An arc-shaped band of thickened sexine extending between two apertures on a pollen grain or spore