斩草除根
zhǎn cǎo chú gēn · HSK 7
to destroy root and branch
🌱🪓 斩 cut + 草 grass + 除 remove + 根 root = chop the weeds, dig out the roots
Four characters spell out the method literally: 斩 chop, 草 grass/weeds, 除 remove, 根 roots. The logic is that cutting a weed at the surface lets it regrow, so you must eliminate the root too — hence destroy something completely, not halfway.
斩 — chariot 车 + axe 斤
Originally depicted execution by chariot-tearing or beheading with an axe — 车 (chariot) plus 斤 (axe). The character came to mean 'to chop, cut off, behead,' and by extension 'to sever decisively.' Modern uses keep this forceful sense, as in 斩断 (sever) and 斩首 (behead).
草 — grass radical 艹 + 早 (zǎo, phonetic)
草 is a semantic-phonetic compound. The top 艹 (grass radical, derived from 艸) gives the meaning 'grass' or 'plant', while 早 underneath supplies the sound. Originally 草 referred to a specific plant and acorn-like fruit, but it shifted to mean grass and vegetation broadly, and by extension 'rough' or 'draft'.
除 — left ear/mound 阝 + surplus 余
除 combines the 'mound/steps' radical 阝 (originally 阜, a hill) with 余 as the phonetic. It first meant the steps of a palace, then extended to 'remove' or 'clear away' (as one sweeps steps clean), and later to mathematical 'divide.'
根 — tree radical 木 + 艮 (phonetic)
根 is a semantic-phonetic compound. The left side 木 ('tree') gives the meaning, since the character originally referred to the roots of a tree. The right side 艮 supplies the sound. From 'tree root' it extended to mean 'root, base, foundation' in general.