The most common and most likely answer to this crossword clue is the 6 letter word TOBAGO
I've seen this crossword clue in The Daily Telegraph
T
O
B
A
G
O
More clues leading to the result TOBAGO
- Also about to seize island
- Part of WI also around corner
- Section of WI also the reverse of 17 down?
- Land inside over island
- Island also contains land
- African country entertaining graduate in Caribbean territory
- Island to leave by boat possibly
- Island also has land in the interior
- To take over an island
- Boat about to leave for Caribbean 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 = tobago.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.