The most common and most likely answer to this crossword clue is the 6 letter word HONSHU
I've seen this crossword clue in The Times
H
O
N
S
H
U
More clues leading to the result HONSHU
- Island house — unfinished hut on poles
- Island featuring in marathons, hundreds!
- Hour on and off to go round on quiet Japanese island
- Island hard on footwear, so I hear
- Part of Japan, hard-working, not quite secure
- Big island’s hard on footwear, so I’ve heard
- Island nearly close after drama backtracking
- Island not entirely perfect and not entirely close
- Some psychopath on Shutter Island
- Hippogryph’s wings fly with nous to island
Buddy explains!

The straight part
We know that "Island" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case island = honshu.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.