General opposites:
* Compasivo/a: This translates to "compassionate" and is a good general opposite of cruel.
* Bondadoso/a: This means "kind" or "good-natured" and also implies the opposite of cruelty.
* Cariñoso/a: This translates to "affectionate" and is a more specific opposite, implying a lack of cruelty in personal relationships.
Opposites related to specific situations:
* Justo/a: This means "fair" and can be the opposite of cruel in situations involving punishment or judgment.
* Misericordioso/a: This translates to "merciful" and is a suitable opposite when referring to acts of cruelty that involve suffering.
* Generoso/a: This means "generous" and can be the opposite of cruel in situations involving a lack of compassion or sharing.
The best word to use will depend on the specific context of your sentence.