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Rubicon

[roo-bi-kon]
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noun
  1. a river in N Italy flowing E into the Adriatic. 15 miles (24 km) long: in crossing this ancient boundary between Cisalpine Gaul and Italy, to march against Pompey in 49 b.c., Julius Caesar made a major military commitment.
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Idioms
  1. cross/pass the Rubicon, to take a decisive, irrevocable step: Our entry into the war made us cross the Rubicon and abandon isolationism forever.
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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for cross the rubicon

Rubicon

noun
  1. a stream in N Italy: in ancient times the boundary between Italy and Cisalpine Gaul. By leading his army across it and marching on Rome in 49 bc, Julius Caesar broke the law that a general might not lead an army out of the province to which he was posted and so committed himself to civil war with the senatorial party
  2. (sometimes not capital) a point of no return
  3. a penalty in piquet by which the score of a player who fails to reach 100 points in six hands is added to his opponent's
  4. cross the Rubicon or pass the Rubicon to commit oneself irrevocably to some course of action
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for cross the rubicon

Rubicon

n.

in phrase to cross (or pass) the Rubicon "take a decisive step," 1620s, a reference to a small stream to the Adriatic on the coast of northern Italy which in ancient times formed part of the southern boundary of Cisalpine Gaul; crossed by Caesar Jan. 10, 49 B.C.E., when he left his province to attack Pompey. The name is from Latin rubicundus "ruddy," in reference to the color of the soil on its banks.

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Online Etymology Dictionary, © 2010 Douglas Harper

cross the rubicon in Culture

cross the Rubicon

[(rooh-bi-kon)]

To make an irrevocable decision; it comes from the name of the river Julius Caesar crossed with his army, thereby starting a civil war in Rome. (See Rubicon.)

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Rubicon

[(rooh-bi-kon)]

A river in northern Italy that Julius Caesar crossed with his army, in violation of the orders of the leaders in Rome, who feared his power. A civil war followed, in which Caesar emerged as ruler of Rome. Caesar is supposed to have said, “The die is cast” (referring to a roll of dice), as he crossed the river.

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Note

“Crossing the Rubicon” is a general expression for taking a dangerous, decisive, and irreversible step.
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Idioms and Phrases with cross the rubicon

cross the Rubicon

Irrevocably commit to a course of action, make a fateful and final decision. For example, Once he submitted his resignation, he had crossed the Rubicon. This phrase alludes to Julius Caesar's crossing the Rubicon River (between Italy and Gaul) in 49 b.c., thereby starting a war against Pompey and the Roman Senate. Recounted in Plutarch's Lives: Julius Caesar (c. a.d. 110), the crossing gave rise to the figurative English usage by the early 1600s.

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Rubicon

see cross the rubicon.

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The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.