To sicken means to become ill or to make someone else feel ill. When you sicken with the flu, you develop symptoms like fever and aches. A spoiled meal might sicken everyone who eats it. Doctors worry about diseases that can sicken whole communities quickly.

The word also describes causing feelings of disgust or revulsion. Cruelty to animals sickens people who care about fair treatment. A sickening smell might make you cover your nose and step away. When someone says “that sickens me,” they mean something offends their sense of what's right or decent so strongly that it almost makes them physically ill.

You might notice sickening used to describe a sudden, unpleasant feeling: “the sickening realization that I forgot my homework” or “a sickening thud when the ball hit the window.” Here the word captures that stomach-dropping feeling when you suddenly understand something bad has happened.

The word carries a sense of things turning wrong, whether in your body, your emotions, or a situation. When something sickens you, it affects you powerfully, either making you physically unwell or disturbing you deeply enough that you feel it almost physically.