WordNet (r) 3.0 (2006):

at rest
    adj 1: in a state of repose or especially sleep
    2: dead; "he is deceased"; "our dear departed friend" [syn:
       asleep(p), at peace(p), at rest(p), deceased,
       departed, gone]

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "at rest":
   abed, asleep, asleep in Jesus, at ease, at home, bereft of life,
   breathless, called home, calm, carrion, cloistered, cool, croaked,
   dead, dead and gone, death-struck, deceased, defunct, demised,
   departed, departed this life, destitute of life, done for,
   dwindling, easy, ebbing, even-tenored, exanimate, fallen, finished,
   food for worms, gone, gone to glory, gone west, halcyon, hushed,
   impassive, in bed, inanimate, isolated, late, late lamented,
   launched into eternity, lifeless, martyred, moldering, no more,
   pacific, passed on, peaceable, peaceful, placid,
   pushing up daisies, quiescent, quiet, relaxed, released, reposeful,
   reposing, restful, resting, resting easy, resting in peace,
   sainted, secluded, sequestered, sequestrated, sheltered, sleeping,
   smitten with death, smooth, still, still as death, stillborn,
   stillish, stilly, stoic, stolid, subsiding, taken away, taken off,
   tranquil, unagitated, underground, undisturbed, unmoved,
   unperturbed, unruffled, unstirring, untroubled, waning,
   with the Lord, with the saints, without life,
   without vital functions