Strong very light wood (5)
I believe the answer is:
balsa
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">strong very light wood</span>' is the definition.<br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for balsa that I've seen before include "lightweight boat-builder" , "Strong lightweight wood" , "Very lightweight wood from tropical tree" , "Raft-making S American corkwood" , "Strong, light wood" .)