円滑
えんかつ · enkatsu · JLPT N1 · na-adj
smoothness
滑 — water radical 氵 + bone 骨
A semantic-phonetic compound: 氵 (water) gives the meaning of slipperiness, while 骨 (bone) supplies the sound. The original sense was 'slippery,' as water makes surfaces hard to grip, and it later extended to 'smooth' and figuratively 'cunning' or 'sly.'