-ize

1.
a verb-forming suffix occurring originally in loanwords from Greek that have entered English through Latin or French (baptize; barbarize; catechize); within English, -ize, is added to adjectives and nouns to form transitive verbs with the general senses “to render, make” (actualize; fossilize; sterilize; Americanize), “to convert into, give a specified character or form to” (computerize; dramatize; itemize; motorize), “to subject to (as a process, sometimes named after its originator)” (hospitalize; terrorize; galvanize; oxidize; simonize; winterize). Also formed with -ize, are a more heterogeneous group of verbs, usually intransitive, denoting a change of state (crystallize), kinds or instances of behavior (apologize; moralize; tyrannize), or activities (economize; philosophize; theorize).
Also, especially British, -ise1 .
Compare -ism, -ist, -ization.
Origin
< Late Latin -izāre < Greek -izein; replacing Middle English -isen < Old French -iser < Late Latin, as above
Usage note
The suffix -ize has been in common use since the late 16th century; it is one of the most productive suffixes in the language, and scores of words ending in -ize are in daily use.
Some words ending in -ize have been widely disapproved in recent years, particularly finalize (first attested in the early 1920s) and prioritize (around 1970). Such words are most often criticized when they become, as did these two, vogue terms, suddenly heard and seen everywhere, especially in the context of advertising, commerce, education, or government—forces claimed by some to have a corrupting influence upon the language. The criticism has fairly effectively suppressed the use of finalize and prioritize in belletristic writing, but the words are fully standard and occur regularly in all varieties of speech and writing, especially the more formal types.
The British spelling, -ise, is becoming less common in British English, especially in technical or formal writing, chiefly because some influential British publishers advocate or have adopted the American form -ize.
British Dictionary definitions for -ize

-ize

suffix
1.
to cause to become, resemble, or agree with: legalize
2.
to become; change into: crystallize
3.
to affect in a specified way; subject to: hypnotize
4.
to act according to some practice, principle, policy, etc: economize
Usage note
In Britain and the US -ize is the preferred ending for many verbs, but -ise is equally acceptable in British English. Certain words (chiefly those not formed by adding the suffix to an existing word) are, however, always spelt with -ise in both Britain and the US: advertise, revise
Word Origin
from Old French -iser, from Late Latin -izāre, from Greek -izein
Word Origin and History for -ize

word-forming element used to make verbs, Middle English -isen, from Old French -iser, from Late Latin -izare, from Greek -izein.

English picked up the French form, but partially reverted to the correct Greek -z- spelling from late 16c. In Britain, despite the opposition (at least formerly) of OED, Encyclopaedia Britannica, the "Times of London," and Fowler, -ise remains dominant. Fowler thinks this is to avoid the difficulty of remembering the short list of common words not from Greek which must be spelled with an -s- (e.g. advertise, devise, surprise).