Rubbery substance (9)
I believe the answer is:
elastomer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">rubbery substance</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 elastomer that I've seen before include "flexible material" , "Stretchy polymer such as rubber" , "rubber-like substance" , "Rubbery substance" .)