Missive

WORD: missive \MIS-iv\, noun

MEANING: A written message; a letter.

USAGE:

She also agreed to write to the Prince, while the Count included a suitably outraged missive of his own.
-- Saul David

Well, somebody sent the invitation, I said, getting back to the mysterious missive.
-- Jane Heller

Missive comes from the Medieval French lettre missive, literally, letter intended to be sent; it ultimately derives from Latin missus, past participle of mittere, to send.