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

Example Sentences

Recent Examples on the Web In less than a second, the entire star turns itself inside out, sending out a shockwave of its own material, racing away at nearly the speed of light. Popular Mechanics, 18 Apr. 2023 Directed energy weapons—like high-energy #lasers—could be used to disrupt or destroy targets at the speed of light. Alain Sherter, CBS News, 17 Apr. 2023 Material accumulates around black holes, is heated to billions of degrees and reaches nearly the speed of light. Ashley Strickland, CNN, 14 Apr. 2023 So in fact, correlations caused by quantum entanglement cannot be used to send signals faster than the speed of light. Juan Maldacena, Scientific American, 1 Nov. 2016 And for internet speeds faster than the speed of light (OK, perhaps not that fast), the AT&T Fiber/DirecTV Stream bundle is the ideal choice. Stefanie Waldek, EW.com, 10 Apr. 2023 In a world where biology moves at the speed of light, those risks can get out of hand. Michael Specter, STAT, 6 Apr. 2023 No – the distance is rate (speed of light) times time (a year). Danya Gainor, CNN, 31 Mar. 2023 The baby black hole would produce jets of highly energetic particles moving near the speed of light, powerful enough to pierce through the remains of the progenitor star, emitting X-rays and gamma rays. Jennifer Ouellette, Ars Technica, 30 Mar. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'speed of light.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

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 9 Jun. 2023.

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

More from Merriam-Webster on speed of light

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