WordNet (r) 3.0 (2006):

pass away
    v 1: pass from physical life and lose all bodily attributes and
         functions necessary to sustain life; "She died from
         cancer"; "The children perished in the fire"; "The patient
         went peacefully"; "The old guy kicked the bucket at the age
         of 102" [syn: die, decease, perish, go, exit,
         pass away, expire, pass, kick the bucket, cash in
         one's chips, buy the farm, conk, give-up the ghost,
         drop dead, pop off, choke, croak, snuff it] [ant:
         be born]
    2: go out of existence; "She hoped that the problem would
       eventually pass away"

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "pass away":
   be all over, be annihilated, be consumed, be destroyed,
   be done for, be gone, be lost, be no more, be superseded,
   be wiped out, become extinct, become void, blow over, cash in,
   cease, cease to be, cease to exist, cease to live, come to naught,
   come to nothing, conk out, decease, dematerialize, demise, depart,
   depart this life, die, die away, die out, disappear, dispel,
   disperse, dissipate, dissolve, do a fade-out, drop, dwindle,
   elapse, end, erode, evanesce, evaporate, exit, expire, fade,
   fade away, fade out, fall, fall asleep, fall into disuse, flee,
   fleet, flit, fly, go, go away, go out, have it, have its time,
   hide, lapse, leave no trace, leave the scene, melt, melt away,
   melt like snow, obsolesce, part, pass, pass on, pass out,
   pass over, peg out, perish, peter out, put off mortality,
   quit this world, retire from sight, return to dust, run its course,
   run out, sink, sink away, stop breathing, succumb,
   suffer an eclipse, superannuate, up and die, vanish,
   vanish from sight, waste, waste away, wear away, wear off,
   yield the ghost