Physical process of heating and hammering metal to strengthen it. Also used metaphorically for rigorous training that forges character or skill.
Forging a sword requires advanced skill.
His mental strength was cultivated through rigorous tempering.
He's had years of tough training, so the cold doesn't bother him.
When he was young, he underwent harsh training from his master.
This player still lacks enough training.
It's a skill acquired through ten years of training.
修行 is training or discipline pursued for spiritual or martial-arts mastery, whereas 鍛え is a broader term that can apply to any skill or metal.
稽古 refers specifically to practice sessions in traditional arts like tea ceremony or kendo, while 鍛え can describe any hardening or disciplining process.
Noun form of the verb 鍛える (きたえる), which originally meant 'to forge metal' and later extended to 'train, discipline'.