A threatening letter refers to a written message that contains an intimidating or harmful message, causing fear or concern for the recipient's safety or well-being. Full definition
Most people begin wondering how debt consolidation works when they are searching for a way to make creditors and debt collectors stop calling and sending threatening letters. (blog.kainscott.com)
I read that he had written threatening letters to the police in one of the newspaper articles about his death. (religion.blogs.cnn.com)
They send threatening letters to the local newspaper, or «7 On Your Side,» and that can sometimes work. (travelmarketreport.com)