Arctic (5)
I believe the answer is:
polar
'arctic' is the definition.
(I know that arctic can be written as polar)
This is all the clue.
(Other definitions for polar that I've seen before include "Directly opposed" , "Relating to icy regions" , "Relating to the Arctic or Antarctic" , "Arctic and Antarctic regions, for example" , "Relating to Earth's coldest regions" .)