徹底
てってい · tettei · JLPT N3 · noun
thoroughness
⛏️ 徹底 = pierce through + bottom: going all the way to the bottom
徹 means to pierce or go through (as in 徹夜, staying up all night), and 底 means bottom (as in 海底, seabed). Doing something 徹底的に means not stopping until you hit the bottom of it.
底 — 广 (shelter radical) + 氐 (phonetic 'dǐ')
底 is a semantic-phonetic compound. The 广 radical depicts a roofed structure or shelter, suggesting the bottom or base of a building. The component 氐 supplies the sound 'dǐ' and originally meant 'low' or 'base,' reinforcing the meaning. Together they convey 'bottom,' 'foundation,' or 'underneath.'