Found in the following dictionaries
SOWPODS (Collins Scrabble Words)
"Rubicon" Definition
noun
A limit that when exceeded, or an action that when taken, cannot be reversed.
Source: Wiktionary
A bounding or limiting line.
Source: Merriam-Webster
One that when crossed commits a person irrevocably.
Source: Merriam-Webster
geographical name
River 15 (24 ) Italy flowing into the Adriatic.
Source: Merriam-Webster