Summarize: v.tr (also -ise)...
Concise (1,800 pages) Oxford English Dictionary, Clarendon Press, Oxford. 9th Ed, 1995. (my copy)
It's actually "ize". We are wrong, not the Yanks. It's been brought in from French (through schools) as an affectation, and from Down Under through the media into mass culture. We've gone over this before on the forum.
Anyway:
<a class="postlink" href="http://en.wikipedia.org/wiki/American_and_British_English_spelling_differences" onclick="window.open(this.href);return false;">http://en.wikipedia.org/wiki/American_a ... ifferences</a>
see: -ise, -ize
"The OED firmly deprecates usage of "-ise" for words of Greek origin, stating, "[T]he suffix..., whatever the element to which it is added, is in its origin the Gr[eek] -ιζειν, L[atin] -izÄre; and, as the pronunciation is also with z, there is no reason why in English the special French spelling in -iser should be followed, in opposition to that which is at once etymological and phonetic."
It goes on to say "... some have used the spelling -ise in English, as in French, for all these words, and some prefer -ise in words formed in French or English from Latin elements, retaining -ize for those of Greek composition."[47] Noah Webster rejected -ise for the same reasons.[48] Despite these denouncements, however, the -ize spelling is now rarely used in the UK in the mass media and newspapers, and is often incorrectly regarded as an Americanism.[49]"