What makes 'cos' unique?

Note: the category and title are both clues and you may need to use some twisted logic as the answer is not straightforward

cos means, besides cosine, Kos, which is an island southwest of Turkey. Kos certainly isn't geographically unique, there are plenty of islands in the area. Is Kos the only island with only three letters in its name? I doubt it. I think I need a hint.

Posted by Tristan on 2003-09-21 11:02:01