ize

1. A verb suffix signifying to make, to do, to practice; as, apologize, baptize, theorize, tyrannize.
   

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.