Source : Webster's Revised Unabridged Dictionary (1913)

Ionian \I*o"ni*an\, a. [L. Ionius. See {Ionic}.]
   Of or pertaining to Ionia or the Ionians; Ionic. -- n. A
   native or citizen of Ionia.

Ionic \I*on"ic\, a. [L. Ionicus, Gr. ?, fr. ? Ionia.]
   1. Of or pertaining to Ionia or the Ionians.

   2. (Arch.) Pertaining to the Ionic order of architecture, one
      of the three orders invented by the Greeks, and one of the
      five recognized by the Italian writers of the sixteenth
      century. Its distinguishing feature is a capital with
      spiral volutes. See Illust. of {Capital}.

   {Ionic dialect} (Gr. Gram.), a dialect of the Greek language,
      used in Ionia. The Homeric poems are written in what is
      designated old Ionic, as distinguished from new Ionic, or
      Attic, the dialect of all cultivated Greeks in the period
      of Athenian prosperity and glory.

   {Ionic foot}. (Pros.) See {Ionic}, n., 1.

   {Ionic}, or {Ionian}, {mode} (Mus.), an ancient mode,
      supposed to correspond with the modern major scale of C.
      

   {Ionic sect}, a sect of philosophers founded by Thales of
      Miletus, in Ionia. Their distinguishing tenet was, that
      water is the original principle of all things.

   {Ionic type}, a kind of heavy-faced type (as that of the
      following line).

   Note: This is Nonpareil Ionic.

Source : WordNet®

Ionian
     n : a member of one of the four divisions of the prehistoric
         Greeks