A formal letter sent to an editor, literary agent or publisher in order to propose an idea for a written work.

Used other than figuratively or idiomatically: see four-letter: containing four letters. / Consisting of or characterised by swear words and profanity.

(US) Of or relating to a fraternity, sorority, or honor society.

(diplomacy) Formal diplomatic letter that appoints a diplomat as ambassador to another sovereign state.

(finance) A publication for investors etc. giving an overview of market conditions.

(historical) a safe-conduct, a document guaranteeing safe passage through hostile territory / a document affirming a person’s lack of a criminal record given as part of a background check

(law) A letter from a settlor to their trustees or a testator to their executors containing non-binding instructions.

Alternative spelling of letter box

plural of letter-box

A type of magical power located within letters, especially of Hebraic, Arabic, or Runic scripts.