Point of no return (7)
I believe the answer is:
rubicon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">point of no return</span>' is the definition.<br/ ><span class="explanation-format__explanation">(as in the phrase 'crossing the Rubicon')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for rubicon that I've seen before include "signifies a famous boundary" , "River crossed by Caesar - no turning back" , "Italy/Gaul boundary" , "River crossed by Caesar in decisive move" , "Line fatefully gone over" .)