The Collaborative International Dictionary of English v.0.48:

Chiliast \Chil"i*ast\, n. [Gr. ?. See Chiliasm.]
   One who believes in the second coming of Christ to reign on
   earth a thousand years; a millenarian.
   [1913 Webster]

WordNet (r) 3.0 (2006):

chiliast
    n 1: a person who believes in the coming of the millennium (a
         time of great peace and prosperity) [syn: millenarian,
         millenarist, chiliast]