Unalterable means it cannot be changed. It is stronger and more final than 'fixed' or 'permanent', because it says changing is not merely difficult but impossible — the door is shut. You meet it with facts, rules, laws, decisions, and the past: an unalterable fact, an unalterable law of nature, an unalterable decision, the unalterable past. It also attaches to firm human qualities — unalterable opposition, an unalterable belief — where it means the person will not be moved no matter what you say. The word is formal and rather grand; it belongs to law, philosophy, contracts, religion, and serious writing, and it sounds heavy in ordinary conversation, where people say 'can't be changed' or 'final'. Two things worth noticing. First, unalterable often carries feeling, not just fact: calling a decision unalterable can be a way of ending an argument, and a listener may hear stubbornness rather than impossibility. Second, alter is a slightly narrower word than change — it suggests adjusting something that stays basically itself, the way a tailor alters a jacket. So unalterable leans towards 'you cannot adjust even a detail of it', which is part of why it feels so absolute.

不可改變的、無法更動的。用在事實、法律、決定上，語氣比 fixed 重得多，等於「板上釘釘」。日常口語多半直接說 can't be changed。