Letter (noun)

1. A written or printed message addressed to someone and usually transmitted by mail.
2. A character representing one or more of the sounds used in speech.
3. A symbol or character used in writing or printing.
4. A formal written communication, typically one sent from one organization to another.

Origin:

Middle english: from old french letre, from latin littera.

Examples:

1. She wrote a letter to her best friend.
2. The letter 'A' is the first letter of the alphabet.
3. In this word, the third letter is 't'.
4. He received a letter from the company informing him of his promotion.
5. The school sent a letter to parents about the upcoming fundraiser.