Someone who's coldhearted is detached and unfeeling. It would be coldhearted to stand there, not caring, when you see a little kid fall and hurt herself.
Most people are sympathetic and warm, but those who don't have much feeling for others are coldhearted. It's coldhearted to blithely hurt someone, and it's coldhearted for a wealthy person to spend money on himself without even thinking about how he can help his needy neighbors. Some days, the world can feel a bit coldhearted. The word first appeared in Shakespeare's play "Antony and Cleopatra," when Antony asks the coldhearted Cleopatra, "Cold-hearted toward me?"
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