Is up north, and that's bad (3)
I believe the answer is:
sin
'bad' is the definition.
(thesaurus)
'is up north and' is the wordplay.
'up north' shows that the letters should be reversed in order (like on a map - reverse order in down clue).
'and' becomes 'n' (common abbreviation for 'and').
'is' backwards is 'si'.
'si'+'n'='SIN'
'that's' acts as a link.
(Other definitions for sin that I've seen before include "It breaches the moral law" , "Pride, say" , "Moral offence" , "Mortal error" , "Err" .)