'Letter' in the Bible

not to be quickly shaken in your mind, nor yet be troubled, either by spirit, or by word, or by letter as from us, saying that the day of Christ had come.

So then, brothers, stand firm, and hold the traditions which you were taught by us, whether by word, or by letter.

If any man doesn't obey our word in this letter, note that man, that you have no company with him, to the end that he may be ashamed.

The greeting of me, Paul, with my own hand, which is the sign in every letter: this is how I write.