數量變成兩倍
看紙變得多厚：對摺一次，厚度剛好兩倍。這一組講的都是數字。
adjective · B2
Two times as big or as many as before. It goes in front of a noun such as increase, rise or drop, and says the number has doubled.
兩倍的
核心畫面
Take a sheet of paper and fold it once. Two things happen in that single movement. The paper is now twice as thick, and it now has two layers. Twofold stands on exactly that fold: look at how much, and it means double; look at how it is made, and it means two parts. The -fold ending is doing the same work in and tenfold.
拿一張紙，對摺一次。這一個動作同時做了兩件事。紙變成兩倍厚，而且紙也多出了兩層。twofold 就站在這一摺上面。往…更多收起
拿一張紙，對摺一次。這一個動作同時做了兩件事。紙變成兩倍厚，而且紙也多出了兩層。twofold 就站在這一摺上面。往「多少」看，它是兩倍。往「怎麼組成」看，它是兩個部分。-fold 這個字尾在 threefold、tenfold 裡做的是同一件事，所以懂了這一摺，整組都懂了。From the word’s history
The source in this packet gives twofold from Middle English twofold and Old English twēofeald, equivalent to two plus -fold. The fold in the spelling is the fold in the picture.
這份資料寫得很清楚：twofold 來自中古英語 twofold、古英語 twēofeald，等於 two 加上 -fold。字面上的「摺」跟畫面裡的那一摺是同一個。
Wiktionary entry for twofold supplied in this packet (kaikki:3f6f69a190036ae4:671778101) — from Middle English twofold, Old English twēofeald, two + -fold
Two branches
由兩個部分組成
看紙變成幾層：同樣那一摺，數的不是厚度而是層數，於是變成「有兩個部分」。
adjective · B2
Made of two main parts. You use it to say that a reason, a problem, a plan or a benefit has exactly two sides to it, and the two sides are usually different from each other.
由兩個部分組成的