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

This is effective because microwaves can cover whole areas at a time, and the beams travel at the speed of light, which is an obvious advantage. — David Szondy july 23, New Atlas, 23 July 2026

From that outer layer, the radiation travels away in all directions at the speed of light, over 186,000 miles per second. — Mike Lynch, Twin Cities, 19 July 2026

Another consequence of the general relativity equations is a region of space around this singularity at which gravity is so extreme that the escape velocity of the area increases to a value greater than the speed of light. — Robert Lea, Space.com, 16 July 2026

And given our understanding of the speed limit of the universe set by the speed of light. — Quanta Magazine, 9 July 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