Fermat's principle


Definition of Fermat's principle

: a statement in optics: the path actually followed by a ray of light undergoing reflection or refraction is one of either minimum or maximum time as compared with adjacent arbitrary paths except for reflection or refraction at an aplanatic surface or passage through an aplanatic lens for which the time is constant

History and Etymology for Fermat's principle

after Pierre de Fermat †1665 French mathematician, its formulator

Love words?

You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

  • More than 250,000 words that aren't in our free dictionary
  • Expanded definitions, etymologies, and usage notes
  • Advanced search features
  • Ad free!

Learn More About Fermat's principle

Dictionary Entries Near Fermat's principle

Fermat's last theorem

Fermat's principle


See More Nearby Entries 

Statistics for Fermat's principle

Cite this Entry

“Fermat's principle.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/Fermat%27s%20principle. Accessed 28 Sep. 2022.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon


Test Your Vocabulary

Commonly Confused Words Quiz

  • vector image of a face with thought expression
  • I went to the ______ store to buy a birthday card.
Spell It

Can you spell these 10 commonly misspelled words?

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!