oculus

n. eye; round opening at the top of a dome (Architecture)

This page is about the architectural term. See also: eye. Oculus (pl. oculi) is the Latin word for eye, and the word 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 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 carried away through drains. In the picture, right, sunlight streams through the opening and strikes the lower part of the dome. The bright opening and the surrounding smooth concrete above the coffering resembles an eye, giving the opening its name.
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Noun
1. the organ of sight
(synonym) eye, optic
(hypernym) sense organ, sensory receptor, receptor
(hyponym) naked eye
(part-holonym) visual system
(part-meronym) choroid, choroid coat
(classification) colloquialism

n. oculus, eye; round opening at the top of a dome (Architecture)

(n.)
An eye; (Bot.) a leaf bud.
  

(n.)
A round window, usually a small one.