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

Definition of Rubicon

 (Entry 1 of 2)

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


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

Definition of Rubicon (Entry 2 of 2)

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

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

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Cite this Entry

“Rubicon.” Dictionary, Merriam-Webster, Accessed 13 Aug. 2020.

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