The Collaborative International Dictionary of English v.0.48:

Millenarian \Mil`le*na"ri*an\, a. [See Millenary.]
   Consisting of a thousand years; of or pertaining to the
   millennium, or to the Millenarians.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Millenarian \Mil`le*na"ri*an\, n.
   One who believes that Christ will personally reign on earth a
   thousand years; a Chiliast.
   [1913 Webster] Millenarianism

WordNet (r) 3.0 (2006):

millenarian
    adj 1: relating to or believing in the millennium of peace and
           happiness [syn: millenarian, chiliastic]
    n 1: a person who believes in the coming of the millennium (a
         time of great peace and prosperity) [syn: millenarian,
         millenarist, chiliast]