I have seen words which are spelled either with a "z" or with a "s" like "optimizer" and " optimiser". I thought that the ones with "z" are wrong but on searching the web I found that both are correct. Why so? Is there any difference in the use also?

2 Answers 2


"-ize" is the common AmE suffix, while in BrE "-ise" is more commonly used:


  • word-forming element used to make verbs, Middle English -isen, from Old French -iser, from Late Latin -izare, from Greek -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached.

  • English picked up the French form, but partially reverted to the correct Greek -z- spelling from late 16c. In Britain, despite the opposition to it (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- (such as advertise, devise, surprise).***


optimise vs optimize usages in AmE vs BrE.

  • And in Canada it's a crapshoot which one you'd see more. Mar 11, 2017 at 20:24
  • @SandyChapman When you type both into your favorite word processor, which, if either, gets flagged as a spelling mistake?
    – Nat
    Mar 12, 2017 at 2:49

According to NGram, both optimizer and optimiser are used in British English. But in American English, the latter isn't used.


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