The Collaborative International Dictionary of English v.0.48:

Autochthon \Au*toch"thon\, n.; pl. E. Authochthons, L.
   Autochthones. [L., fr. Gr. ?, pl. ?, from the land itself;
   a'yto`s self + ? earth, land.]
   1. One who is supposed to rise or spring from the ground or
      the soil he inhabits; one of the original inhabitants or
      aborigines; a native; -- commonly in the plural. This
      title was assumed by the ancient Greeks, particularly the
      Athenians.
      [1913 Webster]

   2. That which is original to a particular country, or which
      had there its origin.
      [1913 Webster] Authochthonic
      Autochthonal

WordNet (r) 3.0 (2006):

autochthon
    n 1: the earliest known inhabitants of a region