The largest of the four main islands of Japan (6)
I believe the answer is:
honshu
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">the largest of the four main islands of japan</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for honshu that I've seen before include "Largest of the islands forming Japan" , "Largest of the Japanese islands" , "Japan's main island" , "Largest island of mainland Japan" , "Largest of the four main islands of Japan" .)