from French -iser, via late Latin -izare from Greek verbs ending in -izein
1 The form -ize has been in use in English since the 16th century; although it is widely used in American English, it is not an Americanism. The alternative spelling -ise (reflecting a French influence) is in common use, especially in British English. It is obligatory in certain cases: first, where it forms part of a larger word element, such as -mise (= sending) in compromise, and -prise (= taking) in surprise; and second, in verbs corresponding to nouns with -s- in the stem, such as advertise and televise.2 Adding -ize to a noun or adjective has been a standard way of forming new verbs for centuries, and verbs such as characterize, terrorize, and sterilize were all formed in this way hundreds of years ago. For some reason, people object to recent formations of this type: during the 20th century, objections were raised against prioritize, finalize, and hospitalize, among others. There doesn’t seem to be any coherent reason for this, except that verbs formed from nouns tend, inexplicably, to be criticized as vulgar formations. Despite objections, it is clear that -ize forms are an accepted part of the standard language.