研ぐ
とぐ · togu · JLPT N1 · verb-godan
to sharpen
🔪🍚 研 = grind/polish, as in 研究 research: polishing knowledge by repeated effort
研ぐ covers sharpening a blade and washing rice (米を研ぐ), since both mean grinding a surface smooth. Its kanji 研 also appears in 研究, research, which is polishing knowledge.