1.Definition: impervious to pleas, persuasion, requests, reason

"Cynthia was inexorable; she would have none of him"

Related Adjective(s):adamant, adamantine, intransigent

2.Definition: not to be placated or appeased or moved by entreaty

"Russia's final hour, it seemed, approached with inexorable certainty"

Related Adjective(s):grim, relentless, stern, unappeasable, unforgiving, unrelenting