笨
bèn · HSK 4
dull
🌳 竹 (bamboo) over 本 (root/tree) — heavy wooden log = dull, clumsy
Decomposition: 竹 'bamboo' on top of 本 'root/trunk of a tree'. A thick wooden block is heavy and slow — hence dull, stupid, cumbersome. The 本 component also hints at the bèn sound.
笨 — bamboo radical 竹 on top + 本 (root/origin)
Originally 笨 referred to the white inner lining of bamboo (竹 'bamboo' + 本 'root/base', which also gives the sound). Over time the meaning shifted from this coarse, plain bamboo material to figurative senses like 'crude,' 'clumsy,' and finally 'stupid' or 'dull-witted' in modern usage.