Being tough, it isn't chow (5)
I believe the answer is:
husky
'being tough' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for husky that I've seen before include "Sledge-pulling dog" , "Arctic sledge dog" , "Sled-dog" , "Arctic sled dog" , "Sledge-dog" .)