Shan’t is the short form of shall not. You glue n’t onto shall: I shall not go becomes I shan’t go. It does the same jobs as shall not — saying that something will not happen, or that you refuse. You will meet it in British books, in older speech, and in children’s stories (“I shan’t!”). Though actually, many young British people almost never say it now; they use won’t. American speakers barely use it at all, except as a joke or when copying British talk. In American school writing, won’t or shall not is what people expect. Keep the apostrophe: shan’t, not shant. It is the same kind of short form as can’t and don’t, only much rarer, and it feels old in a way those two do not.

「shall not」的縮寫（偏英式，現在也偏舊）