Length of sawn timber (5)
I believe the answer is:
plank
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">length of sawn timber</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 plank that I've seen before include "Policy; board" , "Long flat timber" , "Proverbially thick piece of wood" , "Long piece of wood" , "flat piece of timber" .)