To purify means to remove unwanted substances or impurities from something to make it clean, safe, or better quality. When you purify water, you filter out dirt, bacteria, and chemicals so it's safe to drink. When a chemist purifies a substance in a lab, she separates the material she wants from everything else mixed in with it.

The process of purification matters enormously in everyday life. Cities purify their water supply before it reaches homes. Doctors purify medical equipment to kill germs. Refineries purify crude oil to make gasoline and other useful products. Even the air purifiers some families use work by removing dust, pollen, and other particles from the air.

The word can also describe making something morally or spiritually better, though this meaning appears more often in older literature and religious contexts. You might read about a character seeking to purify their soul or conscience.

The noun form is purification. Something that's completely pure, with all impurities removed, is described as purified. A purifier is a device or substance that purifies something, like a water purifier or an air purifier.