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

Times are uncertain for those old-school roughnecks that still go to work every day in the patch; their numbers are much smaller in size as operations move at the speed of light due to efficiency; new workers come in with new skills. —Matt Randolph, Forbes.com, 10 July 2025

These presumably wouldn't have been ejected at the speed of light when Krypton exploded. —Robert Lea, Space.com, 7 July 2025

Moving at the speed of light, radiation from the exploding atom bomb would hit the casing’s inner wall and, in a rebound, flood the interior with a colossal burst of rays that would compress and ignite the hydrogen fuel. —William J. Broad, New York Times, 19 May 2025

But even this monstrous black hole can't stomach so much matter, leading to some serious indigestion in the form of outflows travelling at around 0.27 times the speed of light. —Robert Lea, Space.com, 23 June 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