"Uttermost" means the very greatest, the very furthest, the most extreme — the point past which there is no more. It is almost the same word as "utmost," and in real use they mean the same thing: "he tried his uttermost" = "he tried his utmost." There are two ways it works. As an adjective, before a noun: "the uttermost limit," "the uttermost ends of the earth," "a matter of the uttermost importance." As a noun, with "the": "she did her uttermost to help," "we were pushed to the uttermost." Here is the honest part your dictionary may not tell you: almost nobody says this word today. "Utmost" won. "Uttermost" survives mostly in the Bible, in old poems, in hymns, in law written a hundred years ago, and in people who are reaching for a grand sound — sometimes on purpose, sometimes because they think the longer word must be the stronger one. If a student writes it in an essay, it is not wrong, but it will sound like a costume. It also carries an old physical meaning of "furthest out" (the -most part is the same -most as in "innermost," "topmost"), which is why "the uttermost parts of the sea" sounds right and "the uttermost parts" of an argument does not. So: know it when you read it; write "utmost" or just "greatest."

最大的、極度的；最遠的（等同 utmost，但更古老、更文言，多見於聖經與舊文獻）