When a person is inexorable, they're stubborn. When a thing or process is inexorable, it can't be stopped.
This is a word for people and things that will not change direction. An inexorable person is hard-headed and cannot be convinced to change their mind, no matter what. You can also say that a process, like the progress of a deadly illness, is inexorable because it can't be stopped. A speeding train with no brakes is inexorable; it's not stopping till it crashes. When you see the word inexorable, think "No one's stopping that."