深奥
shēn ào · HSK 7
profound
🌊 深 (deep) + 奥 (mysterious/inner) = deep-and-hidden, so profound and hard to fathom
深 is deep, as in deep water; 奥 means the innermost, mysterious recess of a place. Put deep + innermost together and you get knowledge so deep it is abstruse. Sound: shēn ào, like shun-ow.
深 — water radical 氵 + 罙 (phonetic, depth)
深 combines the water radical 氵 with 罙, which depicts a hand reaching into a cave or hollow. Originally it described deep water, then broadened to mean 'deep' in any sense — distance, color, or feeling. The 氵 gives the meaning, while 罙 hints at both sound and the idea of reaching far in.