Made unfeeling, callous, or cynical, (now) esp. by experience; hard-hearted; hard-bitten.

Of a partisan, an advocate, an enemy: Uncompromising.

Rigid, strict; solemn, formal.

U.S. figurative. Tough; hardened; (also) earthy.

Tough, uncompromising; characteristic of a hard-ass. Cf. hard-ass, n.

figurative or in figurative context: chiefly used attributively with allusion to the qualities of brightness, hardness, coldness, etc…