Tree sap (5)
I believe the answer is:
resin
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">tree sap</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 resin that I've seen before include "viscous material" , "Myrrh, for instance" , "Exudation from fir trees" , "Sticky stuff oozing from trees" , "It's obtained from tree-sap" .)