Cold open after high point (9)
I believe the answer is:
heartless
'cold' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for heartless that I've seen before include "Completely lacking in feeling" , "Lacking feeling through cardiac deficiency" , "Lacking all feelings" , "hard?" , "Cruel and unfeeling" .)