express

Compared meaning: clearly and fully stated (adjective).

比较义项：明确的（形容词）。

• express 本词

  Formal and mainly legal or literary; used only before a noun (express wish, express consent, express purpose), rarely as a predicate; contrasts with something merely implied.

  正式，多见于法律或书面语；只用在名词前（如express wish、express consent、express purpose等固定搭配），很少作表语；强调与“默许、隐含”相对的“明确表示”。

  It was her express wish that no flowers be sent to the funeral.

  这是她明确表示的愿望：葬礼上不要送花。

• explicit

  The everyday, general-purpose word for something spelled out in full detail; can be used before a noun or after 'be'; contrasts with implicit.

  是三者中最通用的词，指把内容说得详细、清楚；既可放在名词前，也可用在be动词后；与implicit（含蓄的）相对。

  The manual gives explicit step-by-step instructions for assembling the furniture.

  说明书给出了组装家具的详细明确的分步说明。

• unequivocal

  The strongest of the three; stresses total absence of doubt or ambiguity, typically describing an answer, statement, or attitude; often used after 'be'.

  三者中语气最强，强调完全没有疑义或含糊；通常用来描述回答、声明或态度，常放在be动词后。

  Her answer was unequivocal: she would never move back home.

  她的回答毫不含糊：她绝不会搬回家里住。

All three mean clearly and fully stated. Express is formal and legal, used only before nouns like wish or consent. Explicit is the general, everyday word, used before a noun or after "be". Unequivocal is strongest, stressing there is no doubt at all.

这三个词都表示“说得清楚、不含糊”，但正式程度和用法不同：express多用于法律或书面语，只放在wish、consent、purpose等名词前；explicit是最通用的词，可修饰说明或陈述，也能放在be动词后；unequivocal语气最强，强调毫无疑义，常用于回答、声明或态度。这里不比较explicit表示“内容露骨（如色情内容）”的义项，也不比较express作动词“表达”或作形容词“特快的”的义项。

Compared meaning: happening or moving quickly (adjective).

比较义项：快速的；迅速的（形容词）。

• fast

  The most general word for speed; it can describe people, vehicles, actions or events, and combines freely with almost any noun without restriction.

  表示“快”时最通用的词，可以形容人、车辆、动作或事件，几乎能与任何名词自由搭配，没有特殊限制。

  A fast car overtook us on the highway just before the exit.

  一辆速度很快的汽车在高速公路出口前超过了我们。

• express 本词

  Used almost only right before certain nouns such as train, delivery or service, meaning a special option faster than the usual one; not used to describe people directly.

  几乎只用在列车、快递、服务等特定名词前，表示比普通选项更快的专项服务；一般不直接用来形容人。

  The express train from the airport reaches downtown in just fifteen minutes.

  从机场出发的特快列车只需十五分钟就能到达市中心。

• quick

  Focuses on an action or event taking little time rather than on pure speed; very common in informal, everyday contexts such as replies or short visits.

  强调动作或事件耗时短，而不是单纯速度快；常见于非正式的日常场合，比如回答或短暂的拜访。

  She gave a quick answer before rushing off to catch her bus.

  她迅速回答了一下，就匆忙跑去赶公交车了。

• prompt

  Emphasizes acting without delay or hesitation, especially when responding to something; typical of formal or business contexts, such as replies or payments.

  强调不拖延、不犹豫地行动，尤其是在回应某事时；常见于正式或商务场合，比如回复或付款。

  The company was known for its prompt replies to every customer complaint.

  这家公司以对每一条客户投诉都能及时回复而闻名。

All four words can mean fast. Fast is the most general word, for people, vehicles, or actions. Quick focuses on an action taking little time. Express goes only before words like train or delivery, not people. Prompt means acting without delay, especially in replies.

这几个词都可表示“快”，但侧重不同：fast 最通用，可形容人、车辆或动作；quick 强调动作耗时短，多用于口语；express 只用在列车、快递等特定名词前表示专项快速服务，不能形容人；prompt 强调不拖延、及时回应，语气偏正式。这里不比较 express 表示“表达（感情）”的动词用法，也不比较 fast 表示“斋戒”的动词用法。