Other forms: missives
A missive usually refers to the old-school style of hand-written communication on paper (remember that?), but these days you also might hear an email called a missive. No matter how you deliver it, a missive is a message.
The noun missive comes from the Latin word missus, meaning "to send." You may have heard the phrase, "fire off a missive," meaning a note, memo or dispatch that was written and sent with urgency and conveyed an important message. It might have been a missive sent from a commander to the troops, telling them of a change in the battle plan. Or, maybe it was an urgent love letter to the commander's wife back home, telling her to tie a yellow ribbon round the ole oak tree...