vicious

An action or behavior that's vicious can cause harm or damage, often intentionally.

When we use "vicious" to describe something or someone, it usually means they're causing trouble, hurting people or things on purpose. You might hear it when talking about a dog that bites someone, attacking without warning - its owners might call the dog vicious. The word can also be used for people who do mean-spirited and hurtful actions repeatedly. For example, saying "she's been vicious with her words all day" would imply she's been being cruel in what she says to others.