The word "malignant" refers to something that is very harmful or dangerous. Most commonly, it is used to describe a type of tumor or cancer that can spread aggressively and negatively affect the health of a person. Moreover, "malignant" can also describe actions or intentions that are malevolent or harmful.
The word "malignant" comes from the Latin word "malignantem," which means "malicious" or "wicked." This itself is derived from "mal-" meaning "bad" and "gnasci," which means "to birth" or "to generate." Thus, it essentially refers to something that generates bad consequences.