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

But the speed of a football play sometimes seems a tick slower than the speed of light, and defensive players often must act without deliberation. — Dan Pompei, New York Times, 23 June 2026

This matter is blasted out at speeds approaching the speed of light as powerful jets that stretch out for thousands of light-years. — Robert Lea, Space.com, 16 June 2026

When the black hole feeds on gas, the object unleashes particles in the form of wind or jets that move at nearly the speed of light, traveling up to thousands of light-years into space. — Jacopo Prisco, CNN Money, 16 June 2026

At present, most large AI models tend to use thousands of graphics processing units (GPUs), constantly exchanging data at the speed of light. — Christopher McFadden, Interesting Engineering, 13 June 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