Prostrate (5)
(Other definitions for prone that I've seen before include "Liable (to suffer) - lying down" , "Lying face downward" , "Placed face down" , "Lying face down or likely to do something" , "Given" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">prostrate</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 lying that I've seen before include "Resting horizontally; fibbing" , "Flat-out" , "So one can't stand" , "Prone - untruthful" , "Untruthful - in bed?" .)