會燒穿東西的
最貼著字根的一家：真的會侵蝕皮膚和材料的東西。
adjective · C1
A caustic substance is strong enough to burn or eat away skin, cloth, metal and other materials by chemical action.
腐蝕性的
核心畫面
Think of a liquid that is cold in the bottle and still burns a hole in your sleeve. Nothing is hot; the stuff simply eats through whatever it touches, and the mark it leaves does not wash out. That is what caustic names. The word then does the same job on words: a caustic line is short, cold and leaves a mark on the person it lands on.
可以想成一瓶摸起來是冷的液體，卻能在袖子上燒出一個洞。沒有火、沒有高溫，它就是把碰到的東西吃掉，留下的痕跡也洗不掉。…更多收起
可以想成一瓶摸起來是冷的液體，卻能在袖子上燒出一個洞。沒有火、沒有高溫，它就是把碰到的東西吃掉，留下的痕跡也洗不掉。caustic 講的就是這件事。後來同一個畫面被搬到話上：一句 caustic 的話很短、很冷，卻會在被講的人身上留下印子。兩邊共用的不是溫度，是「會侵蝕、會留痕」。From the word’s history
Wiktionary traces caustic to Latin causticus, from Ancient Greek kaustikos (burning), from kaustos (burnt). Burning is in the word from the start.
Wiktionary 記錄 caustic 來自拉丁文 causticus，再往前是希臘文 καυστικός（會燒灼的），源自 καυστός（被燒過的）。也就是說，「燒」這件事從一開始就寫在這個字裡。化學的用法離字根最近，講話那個用法則是把同樣的畫面借過去用。
Wiktionary entry 'caustic' (kaikki:3f6f69a190036ae4:676606977), etymology_text: 'From the Latin causticus (burning), from Ancient Greek καυστικός (kaustikós, burning), from καυστός (kaustós, burnt) + -ικός.'
Two branches
會燒到人的話
同一個「會侵蝕」的畫面換到語言上：不是音量大，而是準、利、留得住痕跡。這是一種理解方式，不是說兩個用法有先後的歷史順序。
adjective · C1
A caustic remark criticises someone in a sharp, unkind way that is often clever and funny at the same time.
尖酸刻薄的