poison-pen letter


noun

a letter written in malice, usually anonymously, and intended to abuse, frighten, or insult the recipient

Idioms and Phrases with poison-pen letter

poison-pen letter

A letter, usually anonymous, that makes malicious statements about the recipient or a third party. For example, She told the police about the poison-pen letters, but they said they couldn't pursue the matter. [Early 1900s]