unpaid

Compared meaning: not yet paid (money, bills) (adjective).

比较义项：尚未付清、未偿付的（钱款、账目等）（形容词）。

• outstanding

  More formal; used specifically for debts, invoices, or balances still owed, as in 'outstanding balance/invoice/debt'; rarely describes wages or unpaid labor directly.

  更正式；专门用于尚欠的债务、发票或账户余额，如“outstanding balance/invoice/debt”（未偿余额／未付发票／未偿债务）；很少直接用来形容工资或未获报酬的劳动。

  The company sent her a reminder about the outstanding balance on her account.

  公司给她发了一条关于账户上未偿余额的提醒。

• unpaid 本词

  More neutral and everyday; describes bills, wages, work, or leave that has not been paid, including situations where no payment is expected at all.

  更中性、更常用；可以形容尚未支付的账单、工资、工作，也可以指本来就不给报酬的情况，比如无薪假。

  She took an unpaid leave to care for her sick mother.

  她请了无薪假去照顾生病的母亲。

Outstanding and unpaid both describe money still owed. Outstanding is more formal, used for debts, invoices, or balances, as in 'outstanding balance.' Unpaid is more neutral and everyday, used for bills, wages, or unpaid leave. It does not cover outstanding's other meaning, excellent or remarkable.

这两个词在“尚未付清”这个意义上很接近，但outstanding更正式，多用于债务、发票或账户余额，常见搭配是“outstanding balance/invoice/debt”；unpaid更中性、更口语化，既能形容账单、工资，也能表示“无偿的、不给报酬的”（如无薪假）。这里不比较outstanding的另一常见义项“杰出的、出色的”（如outstanding performance）。

Compared meaning: done freely, without being forced or paid (adjective).

比较义项：出于自愿、不受强迫地做某事，或不获报酬地做某事（形容词）。

• volunteer

  Describes work, roles, or people connected with organized charity or community service; usually placed before a noun (volunteer nurse, volunteer work), and always implies no pay.

  形容与有组织的慈善或社区服务相关的工作、职位或人员；通常放在名词前（如 volunteer nurse、volunteer work），并且总是暗示没有报酬。

  The hospital relies on volunteer nurses to staff the weekend clinic.

  这家医院依靠 volunteer 护士来负责周末诊所的工作。

• willing

  Describes a person's attitude, always followed by 'to + verb'; expresses readiness to do something, without indicating whether the activity itself is paid or organized.

  形容一个人的态度，后面总是接「to+动词」；表示愿意去做某事的心理准备，而不涉及该活动本身是否有报酬或是否有组织性。

  He seemed willing to work extra hours without being asked.

  他看起来 willing 加班，没有人开口要求他这样做。

• voluntary

  A more formal, general word for behavior chosen freely rather than forced; used for decisions, donations, or attendance, and does not necessarily mean unpaid.

  是一个更正式、更通用的词，指出于自由选择而非强迫做出的行为；用于描述决定、捐款或出席情况，不一定意味着没有报酬。

  Attendance at the after-school club is voluntary, not compulsory.

  参加这个课后俱乐部是 voluntary 的，不是强制性的。

• unpaid 本词

  Focuses only on the absence of payment; whether the action was freely chosen is unclear, so it lacks the 'by free choice' meaning shared by the other three words.

  只强调没有报酬这一点；这个行为是否出于自愿选择并不确定，因此缺少其他三个词共有的「出于自由选择」的含义。

  Unpaid overtime is common in this industry, even for staff who never agreed to it.

  在这个行业里，unpaid 加班很普遍，即使员工从未同意过也是如此。

Volunteer, willing, voluntary, and unpaid all relate to free choice or no pay. Volunteer names organized, unpaid charity roles or work. Willing describes a person's attitude, always with 'to' plus a verb. Voluntary means freely chosen, but not necessarily unpaid. Unpaid means simply no payment.

这四个词在「自愿的／不受强迫的」这一义项上很接近，容易混淆：volunteer 和 voluntary 多用来形容有组织的行为或事务；willing 只能形容人的态度，且必须接动词不定式；unpaid 只关心有没有报酬，不一定表示自愿。这里不比较 volunteer 作名词「志愿者」或动词「自愿做」的用法。