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 solution also revealed that a limit should exist around the singularity called the Schwarzschild radius at which the escape velocity of this region of space would exceed the speed of light. —Robert Lea, Space.com, 18 Nov. 2025

This includes the speed of light and Planck’s constant. —Neetika Walter, Interesting Engineering, 17 Nov. 2025

Irrespective of whether gravity itself is inherently quantum in nature, the speed of gravity must be exactly equal to the speed of light. —Big Think, 13 Nov. 2025

Because the speed of light is a constant, two observers moving relative to each other will assign different times to different events. —Adrian Bardon, The Conversation, 12 Nov. 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