- Rubicon - the boundary in ancient times between Italy and Gaul; Caesar's crossing it with his army in 49 BC was an act of war
--1 is a kind of boundary, bound, bounds
- Rubicon, point of no return - a line that when crossed permits of no return and typically results in irrevocable commitment
--2 is a kind of line, dividing line, demarcation, contrast
- Rubicon, point of no return - a line that when crossed permits of no return and typically results in irrevocable commitment