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]

Moby Thesaurus II by Grady Ward, 1.0:

116 Moby Thesaurus words for "disappear":
   abandon, abscond, be all over, be annihilated, be consumed,
   be destroyed, be done for, be gone, be incognito, be no more,
   be past, be unseen, be wiped out, beat a retreat, become extinct,
   blush unseen, bow out, burrow, cease, cease to be, cease to exist,
   clear, come to naught, come to nothing, conk out, dematerialize,
   depart, die, die away, die out, dispel, disperse, dissipate,
   dissolve, do a fade-out, drop from sight, duck out, dwindle,
   elapse, end, erode, escape, escape notice, evacuate, evanesce,
   evaporate, exit, expire, fade, fade away, fade out, flee, fleet,
   flit, fly, go, go away, go into hiding, go on furlough,
   go on leave, go to ground, go underground, have run out, hide,
   hide away, hide out, hole up, lapse, leave, leave no trace,
   leave the scene, lie, lie close, lie doggo, lie hid, lie low,
   lie snug, masquerade, melt, melt away, melt like snow, pass,
   pass away, pass out, peg out, perish, peter out, play peekaboo,
   quit, remain anonymous, remove, retire, retire from sight, retreat,
   run out, sink, sink away, sit tight, slip away, slip off, slip out,
   sneak out, stay in hiding, succumb, suffer an eclipse, take cover,
   take leave, vacate, vanish, vanish from sight, vaporize, waste,
   waste away, wear a mask, wear away, withdraw