磨砺 literally means 'to sharpen on a grindstone' (磨 to grind, 砺 whetstone). It is commonly used figuratively to mean 'to temper oneself through hardship or practice' — similar to 'steeling' or 'honing' one's skills or character in English. You can use it with objects like 刀 (knife) for literal sharpening, or with 自己 (oneself), 意志 (will), or 能力 (ability) for metaphorical tempering.