unyielding

Marilla saw something remarkably like unyielding stubbornness looking out of Anne’s small face.

Whole days have I passed in these Titanic efforts, considering my labor well repaid if, by night-time I had contrived to carry away a square inch of this hard-bound cement, changed by ages into a substance unyielding as the stones themselves; then to conceal the mass of earth and rubbish I dug up, I was compelled to break through a staircase, and throw the fruits of my labor into the hollow part of it; but the well is now so completely choked up, that I scarcely think it would be possible to add another handful of dust without leading to discovery.

With his head thrown back and his lungs burning, he sprinted toward the tape with absolute, unyielding determination.

He commended her exceptional diligence, noting that true cartography requires an unyielding commitment to reality over mere artistic elegance.