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to polish; to shine; to burnish; to scour; to scrub; to brush (teeth); to grind (e.g. a lens)
to refine (a skill, etc.); to improve; to hone; to polish (up); to cultivate (one's character)
毎朝歯を研いている。
I brush my teeth every morning.
古い靴を研いたらきれいになった。
When I polished the old shoes, they became clean.
鏡を丁寧に研くと顔がはっきり見えるようになる。
If you polish the mirror carefully, you can see your face clearly.