Implacable

Part of speech: adjective (a.)

1. Not placable; not to be appeased; incapable of being pacified; inexorable; as, an implacable prince. I see thou art implacable. Milton. An object of implacable enmity. Macaulay.

2. Incapable of ebign relieved or assuaged; inextinguishable. [R.] O! how I burn with implacable fire. Spenser. Which wrought them pain Implacable, and many a dolorous groan. Milton.

Synonyms: Unappeasable; inexorable; irreconcilable; unrelenting; relentless; unyielding.