implacable
"Implacable" is a powerful adjective with essentially one strong, clear meaning — but it's used in a few interesting contexts worth knowing. It describes something or someone that simply cannot be calmed, satisfied, or stopped.
When someone is implacable, no amount of reasoning, apologizing, or negotiating will change their mind or soften their attitude. Think of a person who is so determined or so angry that nothing you do or say makes any difference. They are completely unmovable — like a wall that will not budge no matter how hard you push.
everyday language, literature, formal writing · Formal; common in literature, journalism, and serious writing
You can also use 'implacable' to describe a force, process, or situation that keeps going no matter what — something relentless that cannot be slowed down or resisted. It is often used to give a dramatic, serious tone to writing.
literature, journalism, formal writing · Formal; more common in written than spoken English · figurative