You can picture duty as 'what is owed' — something that falls on you and is expected from your side: the thing you are on the hook for, whether because it is right, because of your job, or because a rule places it on you.
From the word’s history
From Old French deu 'due, owed' (the source of English 'due'), ultimately from Latin debere 'to owe'. The root sense is literally 'what is owed', which is exactly the thread running through every modern sense.
源自古法文 deu「應得的、欠著的」（也是英文 due 的來源），再往上是拉丁文 debere「欠」。字根的意思就是「欠著、該交的」，這條線正好串起下面每一個用法。
etymonline.com/word/duty
登入就可以看每一支怎麼連回核心畫面。
原始詞典資料8 筆記錄
以下是外部詞典記錄的用法，摘錄並精簡格式，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。
Dutyname
- 1
A surname.
dutynoun/ˈdjuː.ti/
- 1
That which one is morally or legally obligated to do.
- Do your duty by me! -No, we don't have a duty to keep you abreast.
- 1805, 21 October, Horatio Nelson England expects that every man will do his duty.
- 2
The state of being at work and responsible for or doing a particular task.
- I’m on duty from 6 pm to 6 am.
- 3
An excise tax; especially, one on imports or exports.
- customs duty
- 4
obsoleteOne's due, something one is owed; a debt or fee.
- Take that which is thy duty, and goo thy waye.
- 5
obsoleteRespect; reverence; regard; act of respect; homage.
- my duty to you
- It [the letter] was written with a plain, unaffected, homely piety that I knew to be genuine, and ended with ‘my duty to my ever darling’—meaning myself.
- 6
engineeringnatural-sciencesphysical-sciencesThe efficiency of an engine in work done per unit of fuel; particularly, the number of pounds of water which a steam pumping engine can raise one foot by burning one bushel or hundredweight of coal.
- 7
The act of urination or defecation, especially for a dog.
- The basic idea in housebreaking is not to wait until the puppy sins and then punish him; it is to call nature to your aid and thus make it easy for him to do his duty.
摘錄自 英文維基詞典 English Wiktionary，已精簡格式；依 CC BY-SA 4.0 授權使用，改動後的內容同樣以此授權提供。