Ru·​bi·​con | \ ˈrü-bi-ˌkän How to pronounce Rubicon (audio) \

Definition of Rubicon

: a bounding or limiting line especially : one that when crossed commits a person irrevocably

Did you know?

In 49 B.C., Julius Caesar led his army to the banks of the Rubicon, a small river that marked the boundary between Italy and Gaul. Caesar knew Roman law forbade a general from leading his army out of the province to which he was assigned. By crossing the Rubicon, he would violate that law. "The die is cast," he said, wading in. That act of defiance sparked a three-year civil war that ultimately left Julius Caesar the undisputed ruler of the Roman world. It also inspired English speakers to adopt two popular sayings -crossing the Rubicon and the die is cast-centuries later. Rubicon has been used in English as the name of a significant figurative boundary since at least the early 1600s.

First Known Use of Rubicon

1613, in the meaning defined above

History and Etymology for Rubicon

Latin Rubicon-, Rubico, river of northern Italy forming part of the boundary between Cisalpine Gaul and Italy whose crossing by Julius Caesar in 49 b.c. was regarded by the Senate as an act of war

Learn More About Rubicon

Time Traveler for Rubicon

Time Traveler

The first known use of Rubicon was in 1613

See more words from the same year

Listen to Our Podcast About Rubicon

Dictionary Entries Near Rubicon




See More Nearby Entries 

Statistics for Rubicon

Cite this Entry

“Rubicon.” Dictionary, Merriam-Webster, Accessed 4 Oct. 2022.

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

More Definitions for Rubicon

Rubicon geographical name

Ru·​bi·​con | \ ˈrü-bi-ˌkän How to pronounce Rubicon (audio) \

Definition of Rubicon

river 15 miles (24 kilometers) long in north central Italy flowing east into the Adriatic Sea


Test Your Vocabulary

Odd Habits and Quirks

  • image1926873504
  • Which of the following best describes an easily irritated person?
Name That Thing

Test your visual vocabulary with our 10-question challenge!

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!