inexorable
adjective
1. not relenting; having no pity; not being or becoming lenient, mild, gentle, or merciful; unyielding.
- Russia's final hour, it seemed, approached with inexorable certainty
Similar word(s): implacable, grim, relentless, stern, unappeasable, unforgiving, unrelenting
2. impervious to pleas, persuasion, requests, reason
- Cynthia was inexorable; she would have none of him
Similar word(s): inflexible, adamant, adamantine, intransigent