missive

Short definition from Wiktionary

Noun

1. 1
   A written message; a letter, note or memo.
2. 2
   Letters sent between two parties in which one makes an offer and the other accepts it.
3. 3
   One who is sent; a messenger.

Adjective

1. 1
   Specially sent; intended or prepared to be sent.
2. 2
   Serving as a missile; intended to be thrown.