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

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Visitors might learn about his various projects, like verifying the speed of light using his television repair equipment and simplifying the table of elements into the Larry Spring Table of Elements. John Metcalfe, The Mercury News, 3 Feb. 2025 Einstein also predicted that when objects accelerate in spacetime, this causes ripples that radiate outward at the speed of light. Robert Lea, Space.com, 20 Jan. 2025 At relativistic speeds — that is near the speed of light — time moves more slowly, which would mean the electron beam wouldn't have enough time to spread out, keeping the beam focused. Victoria Corless, Space.com, 22 Jan. 2025 The ever-changing world of design can be as fickle as the wind, with trends coming and going often at the speed of light. Roger Sands, Forbes, 21 Jan. 2025 See all Example Sentences for speed of light 

Word History

First Known Use

1823, in the meaning defined above

Time Traveler
The first known use of speed of light was in 1823

Dictionary Entries Near speed of light

Cite this Entry

“Speed of light.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/speed%20of%20light. Accessed 16 Feb. 2025.

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

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