Ancient unit of length (5)
I believe the answer is:
cubit
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ancient unit of length</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for cubit that I've seen before include "Ancient linear measure" , "distance" , "Ancient unit of length based on the length of the forearm" , "Elbow-to-finger measure" , "about eighteen inches" .)