磨 ㄇㄛ ˊ mó 杵 ㄔㄨ ˇ chǔ 成 ㄔㄥ ˊ chéng 针 ㄓㄣ zhēn 磨 ㄇㄛ ˊ mó 杵 ㄔㄨ ˇ chǔ 成 ㄔㄥ ˊ chéng 針 ㄓㄣ zhēn to grind an iron bar down to a fine needle (idiom); fig. to persevere in a difficult task to study diligently