General Antonyms:
* Cruel: This is a strong antonym that suggests inflicting pain or suffering.
* Unkind: This is a more general antonym meaning not showing kindness or compassion.
* Mean: This suggests being nasty or unpleasant.
* Harsh: This implies being severe or unsympathetic.
* Ruthless: This suggests a lack of mercy or compassion.
More Specific Antonyms:
* Malicious: This suggests intending to harm or cause suffering.
* Vicious: This implies a fierce and cruel nature.
* Inhuman: This emphasizes a lack of human compassion.
* Thoughtless: This indicates a lack of consideration for others' feelings.
* Selfish: This focuses on caring only about oneself.
The best antonym for "kind" depends on the specific situation and the nuance you want to convey.