speed of light

[ speed uhv lahyt ]

noun

1. Physics, Optics. a fundamental universal constant, the speed at which light and all forms of electromagnetic radiation travel in a vacuum, standardized as 186,282.4 miles per second (299,792,458 meters per second):

   The speed of light, often represented by the letter c, figures prominently in modern physics, as in Einstein’s famous equation E = mc2, which expresses the relation between mass (m) and energy (E).

2. an extremely fast rate:

   They gobbled those appetizers up at the speed of light.

Word History and Origins

Origin of speed of light¹

First recorded in 1820–25