The Collaborative International Dictionary of English v.0.48:

Disappear \Dis`ap*pear"\, v. i. [imp. & p. p. Disappeared; p.
   pr. & vb. n. Disappearing.]
   1. To cease to appear or to be perceived; to pass from view,
      gradually or suddenly; to vanish; to be no longer seen;
      as, darkness disappears at the approach of light; a ship
      disappears as she sails from port.
      [1913 Webster]

   2. To cease to be or exist; as, the epidemic has disappeared.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Disappearing \Dis`ap*pear"ing\,
   p. pr. & vb. n. of Disappear.

   Disappearing carriage (Ordnance), a carriage for heavy
      coast guns on which the gun is raised above the parapet
      for firing and upon discharge is lowered behind the
      parapet for protection. The standard type of disappearing
      carriage in the coast artillery of the United States army
      is the Buffington-Crozier carriage, in which the gun
      trunnions are secured at the upper and after ends of a
      pair of heavy levers, at the lower ends of which is
      attached a counterweight of lead. The levers are pivoted
      at their middle points, which are, with the top carriage,
      permitted restrained motion along the slightly inclined
      chassis rails. The counterweight is held in place by a
      pawl and ratchet. When the gun is loaded the pawl is
      released and the counterweight sinks, raising the gun to
      the firing position above the parapet. The recoil
      following the discharge returns the gun to the loading
      position, the counterweight rising until the pawl engages
      the ratchet.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

disappearing
    n 1: the act of leaving secretly or without explanation [syn:
         disappearance, disappearing] [ant: appearance]