Oculus
Oculus is the Latin word for eye. The word Oculus remains in use in certain contexts, most commonly as the name of the round opening in the top of the dome of the Pantheon in Rome, Italy, and less often in reference to other round windows. The opening of the Oculus in the Pantheon is and has always been open to the weather, allowing rain to enter and fall to the floor, from where it is is carried away through drains in the floor. In this picture, sunlight streams through the opening striking the lower part of the dome. The bright opening and the surrounding smooth concrete above the coffering bears a resemblance to an eye, giving the opening its Latin name Oculus, which is retained.
While Oculus is not in common use in English, words derived from it such as Ocular (relating to the eye) are, primarily in medical and optical fields.
