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

Flight Fiber, an internet service provider that uses fiber-optic cables to send data as fast as 70% of the speed of light, is now available in Westminster. —K. Mauser, Baltimore Sun, 28 July 2025

In a world where AI is generating content at the speed of light, Unreality reminds us of something important: human creativity still matters and deserves a place to shine. —Luciana Paulise, Forbes.com, 31 July 2025

On the extreme end, someone who managed to move at the speed of light would essentially not age compared to someone who is more or less stationary. —Joshua Rapp Learn, Discover Magazine, 31 July 2025

In the present day, every new iteration of the Zoom Vomero 5 — from eye-catching options in deep blue to butter yellow–adjacent styles — is immediately obsessed over, with most fresh arrivals selling out at the speed of light. —Stacia Datskovska, Footwear News, 29 July 2025

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