WordNet (r) 3.0 (2006):

spirit world
    n 1: any imaginary place where spiritual beings (demons or
         fairies or angels or the like) abide; "science has emptied
         the spirit world of its former inhabitants"

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "spirit world":
   bodilessness, ghostliness, immateriality, immaterialness,
   impalpability, imponderability, incorporeality, incorporeity,
   inextension, intangibility, nonexteriority, occult phenomena,
   occultism, otherworldliness, psychical research, psychicism,
   psychics, psychism, shadowiness, spirituality, spirituousness,
   supernaturalism, the occult, unearthliness, unsubstantiality,
   unsubstantialness, unworldliness