研 (Kanji for polish, sharpen)

Onyomi

KEN

KENNY polished his rock with an open hand (holding a chemise cloth)

と*ぐ	to grind or hone - usually a knife. But sometimes you can hone a skill, just like in English. ★☆☆☆☆

研究(けんきゅう)	research ★★★☆☆ 研 (polish, sharpen) + 究 (research) = 研究 (research)
研修(けんしゅう)	study, training ☆☆☆☆☆ 研 (polish, sharpen) + 修 (master a skill) = 研修 (study, training )