Source : Webster's Revised Unabridged Dictionary (1913)

-ize \-ize\ [F. -iser, L. -izare, Gr. ?.]
   A verb suffix signifying to make, to do, to practice; as
   apologize, baptize, theorize, tyrannize.

   Note: In the case of certain words the spelling with -ise
         (after analogy with F. -iser) is the usual form; as,
         catechise, criticise. With regard to most words,
         however, which have this suffix there is a diversity of
         usage, some authorities spelling -ise, others (as in
         this book) -ize.