The Collaborative International Dictionary of English v.0.48:

Achaean \A*ch[ae]"an\, Achaian \A*cha"ian\a. [L. Achaeus,
   Achaius; Gr. ?.]
   Of or pertaining to Achaia in Greece; also, Grecian. -- n. A
   native of Achaia; a Greek.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Achaian
    n 1: a member of one of four linguistic divisions of the
         prehistoric Greeks [syn: Achaean, Achaian]