SINCE 1828
speed of light
noun phraseDefinition of speed of light
: 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
Keep scrolling for more
Comments on speed of light
What made you want to look up speed of light? Please tell us where you read or heard it (including the quote, if possible).
Test Your Vocabulary
Where in the World? A Quiz
-
- What language does pajama come from?
Can you spell these 10 commonly misspelled words?
TAKE THE QUIZ
Test Your Knowledge - and learn some interesting things along the way.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridged
Words at Play
Ask the Editors
Word Games
-
Where in the World? A Quiz
Do you know what languages these words come from?
Take the quiz -
Advanced Vocabulary Quiz
Tough words and tougher competition.
Take the quiz -
Spell It
Can you spell these 10 commonly misspelled words?
Take the quiz -
Add Diction
Build a chain of words by adding one letter at a time.
Play the game
Share speed of light
Resources for speed of light