Cavity, opening (4)
I believe the answer is:
hole
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">cavity</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(hole is a kind of cavity)</span><br/ ><br/ >'<span class="explanation-format__original">opening</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that hole is a type of opening)</span><br/ ><br/ ></span>
(Other definitions for hole that I've seen before include "Nasty place" , "Hollow, cavity" , "excavation" , "depression" , "pocket" .)