Unchangeable means impossible to alter or modify. When something is unchangeable, it stays the same no matter what you do or how hard you try to change it.

Some things in nature are unchangeable: you can't change the fact that water freezes at 32 degrees Fahrenheit, or that the Earth orbits the sun. The past is unchangeable: no matter how much you wish you'd studied harder for yesterday's test or been kinder to a friend last week, what's done is done.

People sometimes call laws or rules unchangeable when they're meant to be permanent, like the laws of physics or certain constitutional rights. But be careful: many things that seem unchangeable actually aren't. People once thought it was unchangeable that humans would never fly, until the Wright brothers proved otherwise. A habit might feel unchangeable until you work hard enough to break it.

The word has a sense of finality to it. When a judge makes an unchangeable decision, there's no appeal or revision possible. When someone has an unchangeable opinion, they've closed their mind completely. Sometimes unchangeable things bring comfort (like knowing the sun will rise tomorrow), and sometimes they challenge us to accept what we cannot control.