Strengthen or support (9)
I believe the answer is:
reinforce
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">strengthen</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(reinforcing is a kind of strengthening)</span><br/ ><br/ >'<span class="explanation-format__original">support</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for reinforce that I've seen before include "give added support" , "Give added strength to" , "provide support" , "Strengthen or support with confrerie" , "Buttress" .)