Old-fashioned letter is a term used to describe a written communication that was sent before the invention of modern technology such as email, text messaging, and instant messaging. The crossword solution for this term is 'RUNE, ' which is a type of letter that was used in ancient times. Runes were symbols that were carved into stone or wood and were used to communicate messages. Runes were used by many cultures, including the Vikings, Celts, and Anglo-Saxons.