The Collaborative International Dictionary of English v.0.48:

Decease \De*cease"\, v. i. [imp. & p. p. Deceased; p. pr. &
   vb. n. Deceasing.]
   To depart from this life; to die; to pass away.
   [1913 Webster]

         She's dead, deceased, she's dead.        --Shak.
   [1913 Webster]

         When our summers have deceased.          --Tennyson.
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         Inasmuch as he carries the malignity and the lie with
         him, he so far deceases from nature.     --Emerson.
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The Collaborative International Dictionary of English v.0.48:

Deceased \De*ceased"\, a.
   Passed away; dead; gone.
   [1913 Webster]

   The deceased, the dead person.
      [1913 Webster]

WordNet (r) 3.0 (2006):

deceased
    adj 1: dead; "he is deceased"; "our dear departed friend" [syn:
           asleep(p), at peace(p), at rest(p), deceased,
           departed, gone]
    n 1: someone who is no longer alive; "I wonder what the dead
         person would have done" [syn: dead person, dead soul,
         deceased person, deceased, decedent, departed]

Moby Thesaurus II by Grady Ward, 1.0:

107 Moby Thesaurus words for "deceased":
   ago, antiquated, antique, ashes, asleep, asleep in Jesus, at rest,
   bereft of life, blown over, body, bones, breathless, by, bygone,
   bypast, cadaver, called home, carcass, carrion, clay, cold, corpse,
   corpus delicti, croaked, crowbait, dated, dead, dead and buried,
   dead and gone, dead body, dead man, dead person, death-struck,
   decedent, defunct, demised, departed, departed this life,
   destitute of life, done for, dry bones, dust, earth, elapsed,
   embalmed corpse, exanimate, expired, extinct, fallen, finished,
   food for worms, forgotten, gone, gone glimmering, gone to glory,
   gone west, gone-by, has-been, inanimate, irrecoverable, lapsed,
   late, late lamented, launched into eternity, lifeless, martyred,
   mortal remains, mummification, mummy, no more, obsolete,
   organic remains, over, passe, passed, passed away, passed on, past,
   pushing up daisies, released, relics, reliquiae, remains, reposing,
   resting easy, run out, sainted, skeleton, sleeping,
   smitten with death, stiff, still, stillborn, taken away, taken off,
   tenement of clay, the dead, the deceased, the defunct,
   the departed, the loved one, vanished, with the Lord,
   with the saints, without life, without vital functions, wound up