Noxious means harmful, poisonous, or extremely unpleasant, especially in a way that affects your health. Noxious fumes from a chemical spill can make people sick if they breathe them in. A factory might release noxious gases that damage the air quality in a neighborhood.

The word carries a sense of real danger beyond mild annoyance. A bad smell might be unpleasant, but noxious fumes are actually hazardous. Scientists might warn about noxious substances in polluted water, or doctors might describe the noxious effects of certain toxins on the body.

You'll also encounter the word describing things that are morally harmful or corrupting. A teacher might talk about the noxious influence of bullying in a classroom, meaning it spreads negativity and hurts everyone. The word suggests something that actively causes damage or harm, whether to your body, your environment, or your community.