The Collaborative International Dictionary of English v.0.48:

ionize \i"on*ize\, v. t. [imp. & p. p. Ionized; p. pr. & vb.
   n. Ionizing.] (Physics, Chemistry)
   To convert (an atom or molecule) into ions, e. g. by
   dissolving in water, by reaction with acid or alkali, or by
   interaction with ionizing radiation. See ionization.
   [Webster 1913 Suppl. +PJC]

The Collaborative International Dictionary of English v.0.48:

ionized \ionized\ adj.
   converted totally or partly into ions. Opposite of
   nonionized and unionized.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

ionized
    adj 1: converted totally or partly into ions [syn: ionized,
           ionised] [ant: nonionic, nonionised, nonionized,
           unionised, unionized]