A word or phrase with a powerful negative connotation used to describe some quality of a person or group is a(n) <u>epithet</u>.
In literature, an epithet is an adjective used to <u>describe a person or a groups of persons</u>. Sometimes, <u>it uses a negative connotation</u> to refer to them, which is why it has been used as a synonym of abuse. However, it is usually used to make it easier to understand or imagine a character.