the.com/oculus

means A round opening, especially a circular window or hole at the top of a dome, that lets in light and air.

from Straight from Latin oculus, meaning 'eye' — the same root that gives us 'ocular' and 'inoculate' (literally 'to put an eye,' as in a bud grafted onto a plant). Architects borrowed the word because a round opening in a dome or wall genuinely resembles a single staring eye, none more famous than the one atop Rome's Pantheon, open to the sky for two millennia.