洞
dòng · HSK 5
cave
🕳️ 氵(water) + 同 (same/tóng) — water carves out a hole; phonetic tóng→dòng
洞 combines the water radical 氵with 同 (tóng), which gives the sound (shifted to dòng) and originally hinted at water hollowing out a cavity. Core senses: hole, cave, aperture — anything bored through.
洞 — water radical 氵 + tóng 同 (phonetic)
洞 is a phono-semantic compound. The water radical 氵 hints at the original sense of a hole or cavity carved out by water, while 同 (tóng) supplies the sound. From 'cave' or 'hollow' it extended to mean 'to penetrate' and figuratively 'to understand thoroughly,' as in 洞察.