One way to hold sworn: the promise has already been spoken out loud, in front of someone, and it cannot be pulled back in. The speaking is over. What is left is the state it put you in. That is why the word is a past participle and why it almost always leans on a word — have sworn, was sworn, be sworn to. Everything else this word does grows out of that one picture: a spoken promise that is now holding something in place.
Wiktionary traces sworn to Old English sworen / ġesworen, the past participle of the verb behind modern swear (Proto-Germanic *swarjaną, to swear), i.e. swear plus the old -en participle ending.
Wiktionary 記載 sworn 來自古英語 sworen、ġesworen，是「發誓」那個動詞的過去分詞，往上接到日耳曼語 *swarjaną，等於 swear 加上古老的 -en 分詞字尾。這條線索跟上面那張畫面一致：字形本身記錄的就是「誓已經發完了」。
Wiktionary (kaikki extract, source_ref kaikki:3f6f69a190036ae4:214535530), etymology_text supplied in evidence packet
Two branches
誓言說出口之後
這一群直接用核心畫面：有人真的開口許了承諾或宣了誓，後面的話語、文件、責任都由那一刻撐著。
verb · B1
The past participle of swear. You use it after have, has or had, and after a form of be, to talk about a serious promise someone has made, an official oath someone has taken, or rude words someone has said in anger.
swear 的過去分詞
像發過誓一樣的敵意
這裡沒有人真的發誓。是把核心畫面借過來形容敵意：講得像立過誓一樣牢，不會改。這是比喻上的連結，不是歷史上的另一條線。
adjective · B2
Used in the phrase sworn enemies: two people, groups, teams or countries that hate each other and go on hating each other for a long time, as if each side had promised never to make peace.
死對頭
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。
swornadj/swɔːn/
Given or declared under oath.
Bound as though by an oath.
Ardent, devout.
這個拼法也被記錄為下列字的變化形：
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。