The Collaborative International Dictionary of English v.0.48:

Elysium \E*ly"sium\, n.; pl. E. Elysiums, L. Elysia. [L.,
   fr. Gr. ?, ? ?, Elysian field.] (Anc. Myth.)
   1. A dwelling place assigned to happy souls after death; the
      seat of future happiness; Paradise.
      [1913 Webster]

   2. Hence, any delightful place.
      [1913 Webster]

            An Elysian more pure and bright than that pf the
            Greeks.                               --I. Taylor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Elysium
    n 1: a place or condition of ideal happiness
    2: (Greek mythology) the abode of the blessed after death [syn:
       Elysium, Elysian Fields]

The Devil's Dictionary (1881-1906):

ELYSIUM, n.  An imaginary delightful country which the ancients
foolishly believed to be inhabited by the spirits of the good.  This
ridiculous and mischievous fable was swept off the face of the earth
by the early Christians -- may their souls be happy in Heaven!