Very light wood (5)
I believe the answer is:
balsa
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">very light wood</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for balsa that I've seen before include "Wood used in model making" , "Something light" , "Strong lightweight wood" , "Strong, light wood" , "Raft-making S American corkwood" .)