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 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

Traveling at the speed of light, this radiation reaches Earth almost instantly, ionizing the upper atmosphere. —Daisy Dobrijevic, Space.com, 28 Mar. 2025

Meanwhile, the longer, bigger flares may occur due to magnetic reconnection events, or when two different magnetic fields collide near the black hole and release energetic particles moving near the speed of light. —Ashley Strickland, CNN, 19 Feb. 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