adamantine
ad.a.man.tine \.ad-*-'man-.te-n, -.ti-n, -'mant-*n\ aj [ME, fr. L adamantinus, fr. Gk adamantinos, fr. adamant-, ]adamas 1: made of or having the quality of adamant 2: rigidly firm : UNYIELDING 3: resembling the diamond in hardness or luster