A person or group that stands firm and plays a crucial supporting role during a crisis; a cornerstone or tower of strength. This idiom originally referred to Mount Dizhu standing firm in the middle of the Yellow River.

to sharpen or hone; to temper or discipline oneself by enduring hardships

A hill formerly located in the middle of the Yellow River at Sanmenxia in Henan province, used metaphorically for firmness and strength

someone or something that stands firm in the face of crisis and plays a crucial role; originally referring to Mount Dizhu standing firm in the torrents of the Yellow River

To hone one's moral integrity and improve one's conduct.

to be at odds or in contradiction with something else

whetstone; whetslate; rubstone