rubicon Meaning, Definition & Usage

noun the boundary in ancient times between Italy and Gaul; Caesar's crossing it with his army in 49 BC was an act of war
noun a line that when crossed permits of no return and typically results in irrevocable commitment
point of no return.

(Anc. geog.) A small river which separated Italy from Cisalpine Gaul, the province alloted to Julius Cæsar. ✍ By leading an army across this river, contrary to the prohibition of the civil government at Rome, Cæsar precipitated the civil war which resulted in the death of Pompey and the overthrow of the senate; hence, the phrase to pass or cross the Rubicon signifies to take the decisive step by which one is committed to a hazardous enterprise from which there is no retreat.