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]

WordNet (r) 3.0 (2006):

disappear
    v 1: get lost, as without warning or explanation; "He
         disappeared without a trace" [syn: disappear, vanish,
         go away] [ant: appear]
    2: become invisible or unnoticeable; "The effect vanished when
       day broke" [syn: vanish, disappear, go away]
    3: cease to exist; "An entire civilization vanished" [syn:
       vanish, disappear] [ant: appear, come along]
    4: become less intense and fade away gradually; "her resistance
       melted under his charm"; "her hopes evaporated after years of
       waiting for her fiance" [syn: melt, disappear,
       evaporate]