A poison-pen letter is a written communication that contains abusive or malicious content, intended to harm or defame the recipient. This type of letter is often used in an attempt to manipulate the recipient's emotions and damage their reputation. Some synonyms for a poison-pen letter include hate mail, spiteful letter, vicious letter, angry letter, nasty note, revenge letter, abusive letter, and malignant letter. These terms are all used to describe written communications that contain harmful or negative content. Poison-pen letters are a type of harassment that can have serious consequences for the recipient and should be taken seriously.