implacable

Not able to be placated or appeased.

He is knight dubb'd with vnhatche'd Rapier, and on carpet conſideration, but he is a diuell in priuate brall, soules and bodies hath he diuorc'd three, and his incenſement at this moment is ſo implacable, that ſatisfaction can be none, but by pangs of death and ſepulcher: Hob, nob, is his word: giu't or take't.

[I]n the reign of Henry the Second, a body happening, by chance, to be dug up near Glastonbury Abbey, without any symptoms of putrefaction or decay, the Welch, the descendants of the Ancient Britons, tenacious of the dignity and reputation of that illustrious hero [King Arthur], vainly supposed it could be no other than the body of their justly-boasted Pen-Dragon; and that he had been immured in that sepulchre by the spells of some powerful and implacable inchanter.

Impossible to prevent or stop; inexorable, unrelenting, unstoppable.

The battleships Washington and South Dakota pushed through the sea with an implacable ease.

Adamant; immovable.

Indeed Cain hated his Brother, becauſe his own works were evil, and his Brothers righteous; and if thy Wife and Children have been offended with thee for this, they thereby ſhew themſelves to be implacable to good; and thou haſt delivered thy ſoul from their blood.