/ ˈruːbɪkən; NAmE -kɑːn/ the Rubicon noun
[ sing. ] the point at which a decision has been taken which can no longer be changed :
Today we cross the Rubicon . There is no going back.
ORIGIN: From the Rubicon , a stream which formed the border between Italy and Gaul. When Julius Caesar broke the law by crossing it with his army in 49BC, it led inevitably to war.