Definition of adamantine:
pigheaded, inconvincible, ossified, opinionated, resist, adamant, iron, mulish, stern, relentless, stiff-necked, remorseless, unyielding, rigid, die-hard, pertinacious, unforgiving, immovable, unbendable, intransigent, self-opinionated, brassbound, hardened, implacable, willful, unappeasable, pat, grim, hard-nosed, unrelenting, headstrong, bullheaded, unbending, hardheaded, uncompliant, obdurate, incompliant, inflexible, self-willed, inexorable, uncompromising, perverse, stubborn, dogged, hard.
- "The Ball and The Cross", G.K. Chesterton.
On that subject, however, she maintained an adamantine reticence, and when I ventured to press her in love's name, she entreated me in tears to forbear, saying that she was bound by an oath which she could not break.- "First Person Paramount", Ambrose Pratt.
- "The Infernal Marriage", Benjamin Disraeli.