Anti means against or opposed to something. When you're anti-war, you oppose war. When someone is anti-pollution, they work against pollution and want to stop it.

It works as a prefix, attaching to the front of other words to show opposition. An antibiotic fights against bacteria in your body. An antidote works against poison. Antifreeze prevents water from freezing in car engines during winter.

You'll see anti attached to all sorts of words: anti-gravity, anti-theft, anti-fog. Sometimes it appears with a hyphen (anti-bullying) and sometimes without (antivirus), depending on what looks clearest.

People also use anti informally to describe someone who opposes a particular idea or movement. If your friend says she's “very anti-homework,” she means she's strongly opposed to it. Groups might organize anti-littering campaigns or become anti-smoking advocates.

The opposite prefix is pro, which means in favor of something. So while an anti-technology person avoids new gadgets, a pro-technology person embraces them. Understanding anti helps you decode countless words: whenever you see it, you know opposition or prevention is involved.