An Oculus, circular window, or rain-hole is a feature of Classical architecture since the 16th century. They are often denoted by their French name, oeil de boeuf, or “bull’s-eye”.

What do you call a window with a rounded top?

Arched Windows The arched window is a decorative style characterized by a rounded top and a flat bottom. Arched windows are typically situated above conventional square- and column-shaped window sets, such as single-hung windows.