A formal letter is a written document that is used to communicate with a specific person or organization. The two crossword solutions for the term formal letter are 'EPISTLE' and 'MISSIVE'. An EPISTLE is a formal letter that is usually written in a literary style, often addressed to a particular person or group of people. A MISSIVE is a formal letter that is typically sent to a large number of people, often as a form of communication from a government or other authority.