speed of light

noun phrase

: a fundamental physical constant that is the speed at which electromagnetic radiation propagates in a vacuum and that has a value fixed by international convention of 299,792,458 meters per second

—symbol c

Examples of speed of light in a Sentence

Recent Examples on the Web

During its orbit, S301 attains speeds more than 100,000 times faster than a commercial airliner—over eight percent the speed of light. — Andrew Paul, Popular Science, 19 Aug. 2026

The technology is used in several kinds of hardware, including optical interconnects, or networks designed to transfer data from AI facilities through glass fibers at the speed of light. — Liz Napolitano, CNBC, 18 Aug. 2026

The Muon g-2 apparatus uses a 50-foot-diameter superconducting storage ring to hold positive muons — technically anti-muons — traveling at nearly the speed of light. — Rupendra Brahambhatt, Interesting Engineering, 15 Aug. 2026

In the future photon propulsion may be able to accelerate a lightweight spacecraft close to the speed of light. — Encyclopedia Britannica, 11 Aug. 2026

Word History

First Known Use

1823, in the meaning defined above

Rhymes for speed of light

• acolyte
• aconite
• allanite
• alunite
• amberlite
• ammonite
• amorite
• amphitrite
• analyte
• anchorite
• andesite
• anhydrite

Kids Definition

speed of light

: a fundamental physical constant that is the speed at which electromagnetic radiation travels in a vacuum and that has a value of 299,792,458 meters per second