Unchangeable (adjective)

Not able to be changed or altered.

Origin:

From un- + changeable.

Examples:

1. The unchanging nature of the laws of physics.
2. His unchangeable opinion on the matter was well known.
3. The unchanging decision of the court was final.
4. The unchanging facts of the case were clear.
5. His unchanging resolve was evident in the way he held himself.