To sharpen or hone a blade or tool (e.g., with a whetstone) to make it edge-cutting.
毎週、包丁を砥石で研いでいる。
I sharpen my kitchen knives on a whetstone every week.
切れ味が悪くなったハサミを丁寧に研いだ。
I carefully sharpened the scissors that had become dull.
職人は刃を研いでから仕事を始める。
The craftsman sharpens the blade before starting work.
To wash rice (rinsing it with water to remove starch and bran).
ご飯を炊く前に米をよく研いでください。
Please wash the rice thoroughly before cooking it.
母はいつも米を三度研いでから炊く。
My mother always washes the rice three times before cooking.
To scour, polish, or burnish a surface by rubbing (e.g., polishing metal or cleaning utensils).
古い鍋の焦げを落とすためにたわしで研いだ。
I scrubbed the burnt stains off the old pot with a scrubbing brush.
銀食器を柔らかい布で研いでピカピカにした。
I polished the silverware with a soft cloth until it shone.