Vicious means deliberately cruel or violent, intended to cause harm or pain. A vicious dog might attack without warning, using its teeth and strength to hurt someone. A vicious rumor spreads lies meant to damage someone's reputation. When someone makes a vicious comment, they're trying to wound the other person emotionally with words chosen to hurt as deeply as possible.

The word suggests more than ordinary meanness. A student might say something unkind without thinking, but a vicious insult is calculated to hurt as much as possible. A vicious attack, whether physical or verbal, shows real intent to harm.

You might hear about a vicious cycle, which describes a situation where one bad thing leads to another, which makes the first thing worse, and so on. For example, not sleeping well makes you tired, which makes it harder to focus in school, which causes stress, which makes it even harder to sleep. Breaking out of a vicious cycle requires stopping the pattern somewhere.