I. ˈrü-bi-ˌkän noun
Etymology: Latin Rubicon-, Rubico, river of northern Italy forming part of the boundary between Cisalpine Gaul and Italy whose crossing by Julius Caesar in 49 B.C. was regarded by the Senate as an act of war
Date: 1626
: a bounding or limiting line ; especially : one that when crossed commits a person irrevocably
II. ˈrü-bi-ˌkän geographical name
river 15 miles (24 kilometers ) N central Italy flowing E into the Adriatic