Hard sweetheart, candid and cold (9)
I believe the answer is:
heartless
'cold' is the definition.
(thesaurus)
'hard sweetheart candid' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'candid' becomes 'artless' (similar in meaning).
'h'+'e'+'artless'='HEARTLESS'
'and' acts as a link.
(Other definitions for heartless that I've seen before include "Scrooge was" , "Callous" , "Lacking pity due to cardiac deficiency" , "Lacking all feelings" , "Lacking feeling through cardiac deficiency" .)