出於自己要，不是被逼
最直接的核心：對照的是「被強迫」。
done by choice · adjective · C1
Done because you choose to do it, not because someone makes you do it.
自願的
核心畫面
You can think of it as: this came from someone's own will — nobody forced it, nobody paid for it; the impulse started inside the person.
一件事的起點在人自己的意願裡。往回追問「為什麼會發生？」，答案不是「上頭規定」、不是「不做會被罰」、也不是「有人付錢…更多收起
一件事的起點在人自己的意願裡。往回追問「為什麼會發生？」，答案不是「上頭規定」、不是「不做會被罰」、也不是「有人付錢」，而是「他自己要」。所以只要看到 voluntary，就可以問一個問題：這個動作是從外面推進來的，還是從裡面長出來的？voluntary 的答案永遠是後者。From the word’s history
From Latin voluntārius "willing, of free will", from voluntās "will, choice", from volō "I want, I will" — the root is literally wanting.
來自拉丁文 voluntārius「出於自由意志的」，字根 voluntās 是「意志、選擇」，再往上是 volō「我要」。也就是說，這個字的字根本身就是「想要」——現代英文所有意思都還牢牢黏在這個「自己要」的核心上，包括連身體動作那個看似很技術的用法。
Wiktionary: voluntary — from Middle English voluntarie, from Old French volontaire, from Latin voluntārius ("willing, of free will"), from voluntās ("will, choice, desire"), from volō ("to will").
Four branches
沒有酬勞的付出
從「不是被逼」再往前一步：不但沒人逼，而且沒人付錢——動機純粹來自自己想幫忙。
unpaid (work or help) · adjective · C1
Used about work or help that people give because they want to, and for which they are not paid.
志願的
身體裡自己控制得了的動作
把「自己要」這個核心搬進身體內部：同一個問題——這個動作是意志發動的，還是自己跑起來的？
voluntary (muscle movement) · adjective · C1
Used about a movement of your body that you can choose to make, because your mind is in control of it.
隨意的
教堂裡的一段風琴音樂
這一支不是從「自願」的比喻長出來的，而是從音樂史的另一條路走過來的，所以不必硬把它拉回核心。
organ piece played in church · noun · C1
A piece of music played in a church, usually on the organ, often just before or after a service.
風琴曲
原始詞典資料9 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。
voluntaryadj/ˈvɒl.ən.tɹi/
- 1
Done, given, or acting of one's own free will.
- September 10, 1828, Nathaniel William Taylor, Sermon delivered in the Chapel of Yale College That sin or guilt pertains exclusively to voluntary action is the true principle of orthodoxy.
- She fell, to lust a voluntary prey.
- 2
Done by design or intention; intentional.
- If a man accidentally kills another by lopping a tree, it is not voluntary manslaughter.
- 3
Working or done without payment.
- Wikimedia is a voluntary service.
- 4
Endowed with the power of willing.
- […] God did not work as a necessary, but a voluntary agent, intending before-hand, and decreeing with himself, that which did outwardly proceed from him.
- 5
Of or relating to voluntarism.
- a voluntary church, in distinction from an established or state church
voluntaryadv/ˈvɒl.ən.tɹi/
- 1
obsoleteVoluntarily.
- And all that els was pretious and deare, / The sea unto him voluntary brings [...].
voluntarynoun/ˈvɒl.ən.tɹi/
- 1
entertainmentlifestylemusicA short piece of music, often having improvisation, played on a solo instrument.
- 2
A volunteer.
- 3
A supporter of voluntarism; a voluntarist.
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。