Tough guy not first to retreat in Arctic region (6)
I believe the answer is:
tundra
'arctic region' is the definition.
(I've seen this before)
'tough guy not first to retreat' is the wordplay.
I cannot really understand how this works, but
'not' could be 'un' (prefix meaning 'not') and 'un' is present in the answer.
'first' could be 'a' (first letter of the alphabet) and 'a' is located in the answer.
This explanation may well be incorrect...
'in' acts as a link.
Can you help me to learn more?
(Other definitions for tundra that I've seen before include "Arctic plain with permanently frozen subsoil" , "Russian countryside?" , "Vast level Arctic region with frozen subsoil" , "wasteland" , "Vast level Arctic regions with frozen subsoil" .)