You can picture shakedown as one movement: someone takes hold of a thing and shakes it hard, so that whatever is loose or hidden falls out. Shake a room, and the hidden things drop. Shake a person, and the money in their pockets drops. Shake a new machine, and the loose bolts and leaks show themselves. Shake a market, and the people who cannot hold on let go. Whatever is still there when the shaking stops is the result. Every use of the word grows out of that one picture.
Our source records that the noun comes straight from the verb phrase shake down, and that a shakedown bed would first have been made by shaking down straw and spreading it flat. That is the most literal use of the phrase; in the other senses the thing being shaken is a person, a place, a machine or a market.
根據 Wiktionary，shakedown 這個名詞是從動詞片語 shake down 直接變來的，而且最字面的一支是把稻草「搖下來」鋪平當床。其他意思裡被搖的就不是稻草，而是人、地方、機器或市場。
Wiktionary (packet source_ref kaikki:3f6f69a190036ae4:1003029355:8490): "Deverbal from shake down. An improvised bed would originally have been made by shaking down straw."
Four branches
搖人、搖地方：把藏著的東西弄出來
這一支離核心畫面最近：被搖的是一個真實的地方或一個真實的人，掉出來的是藏著的東西或口袋裡的錢。兩個意思都被標為口語，也都以美式英文為主。
noun · C1
A very thorough search of a place or of a person, especially a sudden one made by police, guards or officials who are looking for things that are hidden.
徹底搜查
搖新東西：把毛病搖出來，搖到穩
被搖的東西從「藏東西的地方」換成「剛做好、還沒信得過的新東西」，掉出來的不是秘密，而是毛病。
noun · C1
A last test of a new boat, plane, vehicle or system, run in real working conditions before it goes into normal use, so that any faults still left in it come out.
試航／試運轉
搖完之後，剩下什麼
前面兩支看的是「掉出來的東西」，這一支把鏡頭轉到另一邊：搖完之後還留在場上的是誰、是什麼。
noun · C2
A period of time when prices on a financial market are falling. It usually suggests a sharp drop over a stretch of days or weeks rather than a slow, steady decline.
行情下殺、跌勢
把稻草搖下來鋪成床
這一支不是從「搖出秘密」的比喻延伸來的，而是 shake down 最字面的一種結果：搖下來的東西本身就是要用的。
noun · C2
A bed made quickly on the floor out of whatever is at hand, for someone who has nowhere else to sleep. You mostly meet this use in older writing.
臨時打的地舖