Jemmy, lever (7)
I believe the answer is:
crowbar
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">jemmy</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">lever</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(crowbar is a kind of lever)</span><br/ ><br/ ></span>
(Other definitions for crowbar that I've seen before include "Heavy iron lever" , "In America, one prizes" , "Burglar's tool, perhaps" , "Powerful opener" , "Iron lever for prising" .)