Cruel; unfeeling (9)
I believe the answer is:
heartless
This clue is a double definition.
'cruel' is the first definition.
(similar in meaning)
'unfeeling' is the second definition.
(I've seen this in another clue)
(Other definitions for heartless that I've seen before include "Without pity or feeling, being defective in cardiac way" , "Cold-blooded" , "Unkind" , "with no concern for others?" , "Uncaring" .)