The correct spelling of the word is "set in stone" and it means something that is fixed or firmly established. The "in" is pronounced as "ɪn" and the "stone" as "stoʊn". Sometimes, people might misspell it as "set one ways" due to the similar sound of "in" and "one". However, it is important to use the correct spelling to avoid confusion and convey the intended meaning of the phrase accurately.