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

That began to change around the turn of the millennium, when physicists started smashing gold ions together at nearly the speed of light inside the giant particle accelerator at Brookhaven National Laboratory on Long Island in New York State. — Clara Moskowitz, Scientific American, 28 Sep. 2026

The quest for real-life warp drives Einstein taught us that objects with mass can't accelerate through space beyond the speed of light, according to his theory of special relativity. — Micah Hanks, Space.com, 23 Sep. 2026

Extreme nuclear matter RHIC operated at BNL from 2000 to 2026 and was designed to investigate exotic forms of nuclear matter by colliding heavy atomic nuclei, like gold, at nearly the speed of light. — Georgina Jedikovska, Interesting Engineering, 23 Sep. 2026

Every second, particles zip through your body at nearly the speed of light. — Jesse Liu, The Conversation, 14 Sep. 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