(bound form) to temper metal by heating it and then dipping it into water or oil to increase hardness

To heat a substance to remove impurities, extract a component, or strengthen it; to smelt, refine, or temper

(bound form) to sharpen or hone, such as a blade or one's own skills and character

To improve one's character, skills, or physical fitness through practice or experience; often confused with 练 liàn