Cold bum sanitised with soap (13)
I believe the answer is:
dispassionate
'cold' is the definition.
(thesaurus)
'bum sanitised with soap' is the wordplay.
'bum' indicates anagramming the letters (bum can mean faulty or wrong).
'with' means one lot of letters go next to another.
'sanitised' put after 'soap' is 'soapsanitised'.
'soapsanitised' is an anagram of 'DISPASSIONATE'.
(Other definitions for dispassionate that I've seen before include "Rational, impartial" , "Imperturbable" , "Not affected by personal feelings" , "Objective, unemotional" , "taking the unbiased view?" .)