To make someone feel very ill or disgusted.
The word sicken can make people think of feeling very bad or wanting to throw up.
Examples:
The bad smell will sicken you.
The sight of blood can sicken some people.
Eating too much candy can sicken your stomach.
The taste of the medicine sickened him.
The thought of eating bugs might sicken some people.
The news of the accident sickened everyone who heard it.