攻こう玉ぎょく

noun

cultivating knowledge and virtue; jewel polishing

Poetic term. Literally 'polishing a jewel', used metaphorically for refining one's character or intellect through study and effort. Rare in modern everyday language.

• 「他た山ざんの石いし以もって玉たまを攻おさむべし」という故こ事じに由ゆ来らいする言こと葉ばで、攻こう玉ぎょくは人じん格かくを磨みがくことを意い味みする。

  Derived from the proverb 'Use a stone from another mountain to polish your own jewel,' 攻玉 means refining one's character.