Adamantine
Adamantine ad·a·man·tine | \ ˌa-də-ˈman-ˌtēn , -ˌtīn, -ˈman-tᵊn Definition of adamantine: 1: made of or having the quality of adamant 2: rigidly firm: UNYIELDING adamantine discipline 3: resembling the diamond in hardness or luster Context: For all the seeming relentlessness of the rise of China under and increasingly adamantine authoritarianism, politics can pack surprises that suddenly change the country's trajectory. Source: The Economist , The darkest corners, March 6-March 12, p.12