The Collaborative International Dictionary of English v.0.48:

Preadamite \Pre*ad"am*ite\, n. [Cf. F. pr['e]adamite.]
   1. An inhabitant of the earth before Adam.
      [1913 Webster]

   2. One who holds that men existed before Adam.
      [1913 Webster]

The Devil's Dictionary (1881-1906):

PRE-ADAMITE, n.  One of an experimental and apparently unsatisfactory
race that antedated Creation and lived under conditions not easily
conceived.  Melsius believed them to have inhabited "the Void" and to
have been something intermediate between fishes and birds.  Little its
known of them beyond the fact that they supplied Cain with a wife and
theologians with a controversy.