透
toù · HSK 4
to penetrate
💨 透 = 辶 (walk) + 秀 (xiù, slender/excel); walking right through to the other side
The 辶 radical means motion or walking, and 秀 lends the sound (xiù shifted to tòu). Together: motion that goes all the way through — penetrate, pass through, thoroughly.
透 — walk radical 辶 + 秀 (xiù, elegant/phonetic)
透 is a semantic-phonetic compound. The walk radical 辶 suggests movement or passing through, while 秀 supplies the sound. The original sense was 'to pass through' or 'penetrate,' which extended to meanings like 'thoroughly,' 'transparent,' and 'leak through.'