Definition of missives:
(n) :
(formal) A written message; a letter, note or memo.
(adj) :
Specially sent; intended or prepared to be sent.
(n) :
(in the plural, Scots law) Letters sent between two parties in which one makes an offer and the other accepts it.
(n) :
(obsolete) One who is sent; a messenger.
(adj) :
(obsolete) Serving as a missile; intended to be thrown.