Ru ‧ bi ‧ con /ˈruːbɪkən, -kɒn $ -kɑːn/ BrE AmE noun
[ Date: 1600-1700 ; Language: Latin ; Origin: Rubico river in northern Italy which Julius Caesar crossed in 49BC, setting off a civil war ]
cross the Rubicon to do something that will have extremely important effects in the future and that you cannot change