The Oculus at Sainte-Chapelle.
When I went to Paris a few years ago, one of my favorite places (besides the catacombs) was the King's chapel at Sainte-Chapelle. There were beautiful stained-glass windows as far as the eye could see, but the circular one shown in the photo had particularly caught my eye. Today, I learned that the beautiful, round window was called an Oculus. Oculus is defined as "round window, especially over the main door in a church," "A round or eye-like opening or design," or "a circular aperture." Oculus is the Latin word for "Eye," and it does have a few other meanings, but I want to stick with the window variety. As far as I can tell, it was first used in this context around 1848. Oculus is a noun and can be fairly easy to use when writing. Some examples may include:
"The Oculus at the St. Mary's Cathedral contained the entire story of Christ within its circular frame." "She peered out of the Oculus as she waited for her love to return." "I see that the Oculus has been redone. What a relief to have some natural light in here for a change."
There you have it! To learn more, visit: The Phrontistery, Merriam-Webster, Vocabulary, The Oxford Dictionary, and The Collins Dictionary. The photo is my own.