firmament

American  

[fur-muh-muhnt] / ˈfɜr mə mənt /

noun

1. the vault of heaven; sky.

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firmament British  

/ ˈfɜːməmənt, ˌfɜːməˈmɛntəl /

noun

1. the expanse of the sky; heavens

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Other Word Forms

• firmamental adjective

Etymology

Origin of firmament

1250–1300; Middle English < Late Latin firmāmentum sky, Latin: support, prop, stay, equivalent to firmā ( re ) to strengthen, support ( firm ² ) + -mentum -ment

Explanation

The firmament is the curve of the sky, especially if you imagine it as a solid surface. You can describe the sky at night as a firmament shining with stars (if you're feeling poetic). The word firmament comes from the Latin firmus, or "firm," and this description of the sky as something solid reflects ancient ideas of the way the universe was constructed. The first stargazers imagined the sky as a sphere, and it wasn't until the late 1500s that the idea of an infinite universe was seriously considered. Today the word firmament is mostly literary, used to poetically describe the visual curve of the sky.

Example Sentences

Let’s take a moment to appreciate the cabin headliner, twinkling like thousands of LED stars in the firmament.

From The Wall Street Journal • Apr. 4, 2026

A century on, the place of all three in the firmament is secure.

From The Wall Street Journal • Nov. 14, 2025

Not all of our stars are onscreen; more than two dozen are in the Michelin firmament.

From Los Angeles Times • Aug. 8, 2025

The cast - and the status of the 1922 original in the film firmament - means Eggers' movie had achieved a cult-like following even before its release.

From BBC • Dec. 31, 2024

Above in the night the sparks from the funnels spiraled upward to join the firmament of stars.

From "Secrets at Sea" by Richard Peck