The antonyms for the word "kind-hearted" are numerous and range from harsh to cruel. One antonym could be unkind, which means lacking in sympathy or kindness. Another antonym could be mean-spirited, which means having a disposition to do harm or cause trouble. A third antonym could be uncharitable, which means lacking in compassion or generosity. Similarly, callous, ruthless, and malevolent are also possible antonyms for the word "kind-hearted." These words describe an individual who is cold, harsh, and insensitive to the needs and feelings of others. In contrast, being kind-hearted is a valuable and admired trait that enables people to help others and spread joy and happiness.