Word Origin & History
suffix forming verbs, M.E. -isen, from O.Fr. -iser, from L.L. -izare, from Gk. -izein. English picked up the Fr. form, but partially reverted to the correct Gk. -z- spelling from late 16c. In Britain, despite the opposition (at least formerly) of OED, Encyclopaedia Britannica, 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 (advertise, devise, surprise) which must be spelled with an -s-.