letter

noun:a written or printed communication addressed to a person or organization, typically sent by mail
- She received a heartfelt letter from her grandmother.
noun:a character representing one or more of the sounds used in speech; any of the symbols of an alphabet
- The word 'cat' begins with the letter 'c'.
noun:the precise terms of a statement or requirement; the strict verbal interpretation
- He followed the instructions to the letter.
noun:a written notice used in business transactions, such as a letter of credit or a letter of intent
- The exporter required a letter of credit from the importer before shipping the goods.