Epistle (noun)

1. A letter, especially an official or formal one.
2. A literary work in the form of a letter, often written in a didactic or persuasive style.

Origin:

From the latin word epistula, which means "letter".

Examples:

1. He wrote an epistle to his friends.
2. The epistle was written by the apostle Paul.
3. The epistle contains important teachings about the Christian faith.
4. He received an epistle from his estranged wife.
5. The epistle was addressed to the church in Corinth.