Volcano's mouth (6)
I believe the answer is:
crater
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">volcano's mouth</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 crater that I've seen before include "Great hole as on top of volcano" , "Caldera" , "Bowl-shaped mouth of volcano" , "Lunar surface dent" , "Fissure in the earth's crust" .)