from Wiktionary, Creative Commons Attribution/Share-Alike License
- The future is determined; there are no more options; events will proceed in an irreversible manner; the point of no return has been passed.
from the GNU version of the Collaborative International Dictionary of English
- n. the hazard must be run; the step is taken, and it is too late to draw back; the last chance is taken.
From games of chance in which the outcome is determined by the throwing of dice or a single die. Popularized by its use by Julius Caesar when he crossed the Rubicon to begin a civil war in the Roman Republic, indicating the commission of an irreversible act, from whence also cross the Rubicon. (Wiktionary)