润
rùn · HSK 7
moist
💧 氵(water) + 闰 = water makes things moist; the 氵 radical signals moisten/lubricate
The left side 氵 is the three-drop water radical, marking anything wet, so 润 means moist or to moisten. The right side 闰 (rùn, leap) is purely the sound clue. Same rùn sound, same 闰 part as in 闰年 leap year.
润 — water radical 氵 + run/king 闰
A semantic-phonetic compound: 氵 (water) gives the meaning, while 闰 (rùn) supplies the sound. The original sense was 'to moisten' or 'to soak,' which extended to 'glossy,' 'sleek,' and figuratively 'to enrich' or 'profit.'