人被打到倒下
最貼近字面的一家：真的有東西倒下去。
noun · B2
In boxing, the moment when a fighter is hit and goes down onto the floor of the ring.
擊倒倒地
核心畫面
You can picture knockdown as one short movement: something is struck, and it goes down. A boxer goes down onto the floor of the ring. A price is pushed down until it looks like a bargain. An argument puts the other side down so they cannot answer. A is taken down into flat pieces and carried away. In a lab, a gene's activity is turned down until it is quiet. The two parts of the word stay visible the whole time — knock, then down — so the useful question in a new sentence is simply: what is being sent here?
「knockdown」可以想成一個很短的動作：被敲一下，然後往下掉。拳擊手倒在地板上。價錢被壓到看起來像撿到便宜。一…更多收起
「knockdown」可以想成一個很短的動作：被敲一下，然後往下掉。拳擊手倒在地板上。價錢被壓到看起來像撿到便宜。一個論點把對方壓得答不出話。櫃子被拆成一片一片放平帶走。實驗室裡，基因的活性被調低到幾乎沒聲音。這個字的兩個部分一直看得見：knock（敲）和 down（往下）。所以遇到新句子時只要問一件事：這次被打下去的是什麼？From the word’s history
The source gives the word as knock + down, with no older story behind it. The modern uses all keep both parts in view.
來源資料只說這個字是 knock 加 down 組成的，沒有更早的故事。今天每一個用法，兩個部分都還看得見。
Wiktionary entry for knockdown, etymology_text supplied in this packet: "From knock + down." (source_ref kaikki:3f6f69a190036ae4:830043226)
Three branches
把數值往下壓
被打下去的不是人，是一條看不見的高度：價格、活性。
adjective · B2
Used about a price: much lower than the usual price, low enough that the thing looks like a bargain.
超低價的
拆成一片一片
往下的方向變成「拆下來、放平」，而且是設計好的，不是壞掉。
adjective · C1
Made so that it can be taken apart into flat pieces for packing or carrying, and then put together again.
可拆組的