The antonyms for the word tender-hearted are ruthless, callous, unfeeling, heartless, and insensitive. These words depict a person who is not compassionate, lacks empathy, and is incapable of showing kindness or emotions. Ruthless implies a disregard for others' feelings and an inclination towards cruelty, while callous suggests a cold, indifferent demeanor. Unfeeling and insensitive both connote a lack of awareness or concern for others' emotions. Heartless signifies a complete absence of compassion, while brutal implies intense aggression towards others. Overall, these antonyms for tender-hearted describe someone who is the complete opposite of kind, compassionate, and empathetic.