Lightweight timber (5)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lightweight 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 balsa that I've seen before include "A slab (anag.)" , "Strong lightweight wood" , "lightweight boat-builder" , "Wood used by model makers" , "Lightweight timber" .)
(Other definitions for scrub that I've seen before include "insignificant type" , "Curbs (anag.)" , "Do away with" , "Clean thoroughly - cancel" , "Clean by rubbing really hard" .)