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

The star's orbital energy provides enough juice to heat the gas in the disk and then expel a quantity of material equivalent to Jupiter's mass at velocities up to 15% of the speed of light. —Keith Cooper, Space.com, 9 May 2025

In today's dynamic digital world, with information flowing at the speed of light, the meaning of online reputation management (ORM) has completely changed. —Chris Hinman, Forbes.com, 21 Apr. 2025

The hyperbole of Robinson hitting baseballs a country mile and stealing bases at the speed of light. —Jaylon Thompson, Kansas City Star, 16 Apr. 2025

In our current times, when words play such a colossal role, when the world is literally filled with typewriters and printers, when billions of words are disseminated daily at the speed of light, the tragedy of words cannot be waved aside. —Isaac Bashevis Singer, Harpers Magazine, 26 Mar. 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