Last but one (11)
I believe the answer is:
penultimate
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">last but one</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for penultimate that I've seen before include "Next to last" , "Last-but-one" , "Not quite the last" , "not quite at the rear" , "Last but one" .)