The Collaborative International Dictionary of English v.0.48:

Missive \Mis"sive\, a. [See Missive, n.]
   1. Specially sent; intended or prepared to be sent; as, a
      letter missive. --Ayliffe.
      [1913 Webster]

   2. Missile. "The missive weapons fly." --Dryden.
      [1913 Webster]

   Letters missive, letters conveying the permission, comand,
      or advice of a superior authority, as a sovereign. They
      are addressed and sent to some certain person or persons,
      and are distinguished from letters patent, which are
      addressed to the public.
      [1913 Webster]