-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.

Source: Webster's Revised Unabridged Dictionary (1913)