flint

(noun) a hard kind of stone; a form of silica more opaque than chalcedony.

(noun) a river in western Georgia that flows generally south to join the Chattahoochee River at the Florida border where they form the Apalachicola River. Synonyms: Flint, Flint River.

(noun) a city in southeast central Michigan near Detroit; automobile manufacturing. Synonyms: Flint.

(adj) showing unfeeling resistance to tender feelings. Synonyms: flinty, granitic, obdurate, stony. Examples: "His flinty gaze." "The child's misery would move even the most obdurate heart."