可以隨意花用
最貼近字根的一層：這筆錢在你手上，你可以自由處置。
disposable income · adjective · C2
Available to be used, especially money you still have after paying for the things you need.
可支配的
核心畫面
A way to picture it: something you are free to do what you like with. Dispose of it, or dispose it as you please — it is at your disposal.
「你可以隨你高興處置的東西」：它擺在你手上，要留、要用、要丟，決定權在你。這個字的根 dispose 本來就是「安排…更多收起
「你可以隨你高興處置的東西」：它擺在你手上，要留、要用、要丟，決定權在你。這個字的根 dispose 本來就是「安排、處置」，-able 加上去就是「可以被這樣處置的」。所以 disposable 底層講的不是「垃圾」，而是「處置權在使用者這邊」——只是這個自由往兩個方向長：一個方向是「我可以隨手丟」，另一個方向是「我可以隨意花用」。From the word’s history
dispose (from French disposer, to arrange or deal with) + -able (from Latin -ābilis, 'able to be') — able to be dealt with as one chooses.
dispose 來自法語 disposer（安排、處置），字尾 -able 由拉丁語 -ābilis 經古法語 -able 進入英語，意思是「可以被…的」。合起來就是「可以被任意處置的」——這個「處置」的自由度正是現代兩個意思共同的出發點。
The entry's own etymology tree: French disposer + Latin -ābilis > Old French -able > Middle English
Two branches
用完就丟
同樣是「隨你處置」，但這裡的處置窄化成一種：dispose of it，丟掉它。
meant to be thrown away · adjective · C2
Made to be used once, or for only a short time, and then thrown away.
拋棄式
原始詞典資料5 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
disposableadj/dɪsˈpəʊzəbl̩/
- 1
That can be disposed of.
- 2
That is designed to be discarded rather than reused, refilled or repaired.
- Rather than purchase an expensive razor he bought a packet of cheap disposable ones.
- A disposable cup sits in a museum gallery, fully intact even after being cast aside thousands of years ago.
- 3
Available to be used; at one's disposal.
- disposable income
disposablenoun/dɪsˈpəʊzəbl̩/
- 1
Any object that is designed to be disposed of, rather than refilled or repaired.
- Parents who use cloth diapers often use disposables for travel, nights, or both.
- Durable goods can be cost-effective but make great disease vectors, and disposables like syringes and needles can be a problem in the poorest places, where there's desperate need of vaccines for diseases like polio. That's where the UCSD scientists come in.
- 2
Any object that is designed to be disposed of, rather than refilled or repaired.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。