Island not entirely perfect, not entirely close either (6)

I believe the answer is:

honshu

I'm a little stuck... Click here to teach me more about this clue!

'island' is the definition.
(Honshu is an example)

I don't understand the rest of the clue.

(Other definitions for honshu that I've seen before include "Largest of the islands forming Japan" , "The largest island unit of Japan" , "Largest of the four main islands of Japan" , "Japan's main island" , "Largest island of Japan's mainland" .)

I've seen this clue in The Hindu.

Want a hint initially instead of a full solution? Install my app