# oculus

/ˈɒkjʊləs/ (UK) · CEFR C2 · Noun

Source: https://englishreference.com/word/oculus
Updated: 2026-05-07

## Definition

a round opening or window in the center of a dome or wall. It lets light and air into a building, often at the very top of a ceiling.

For teachers: a circular opening at the apex of a dome or in a wall. Derived from the Latin word for 'eye', it serves to admit light and reduce the structural weight of the masonry.

## Examples

- Light streams through the oculus at the top of the dome.
- The architect designed a large oculus to illuminate the central hall without the need for traditional side windows.
- Rainwater falling through the unglazed oculus of the Pantheon is efficiently managed by a sophisticated drainage system built into the slightly slanted marble floor below.

## Usage notes

- The plural form is 'oculi'.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.