act

Compared meaning: to behave or perform in a certain way (verb).

比较义项：以某种方式行事、表现（动词）。

• act 本词

  The most general and common of the three; simply means to do something or behave in a way, with no judgment about whether it is proper. Can stand alone or take an adverb.

  三者中最常用、最中性的词；只表示“做某事、以某种方式行事”，不带对是否得体的评判。可单独使用，也可加副词。

  Stay calm and act quickly if the fire alarm goes off.

  如果火警响起，要保持冷静，迅速行动。

• behave

  Implies conforming to proper or polite standards of conduct, often said of children or manners; frequently used alone as a command, 'behave (yourself)'.

  强调符合得体、有礼貌的行为标准，常用于谈论小孩或礼仪；常单独用作命令句“behave (yourself)”（规矩点）。

  The teacher warned the kids to behave themselves on the school trip.

  老师警告孩子们在学校郊游时要规规矩矩。

• acquit

  Formal and less common; almost always reflexive with an adverb ('acquit oneself well/admirably'), describing how someone performs under a difficult test or challenge.

  较为正式、不常用；几乎总是反身用法并搭配副词（acquit oneself well/admirably），描述某人在艰难考验或挑战中的表现。

  The rookie acquitted himself well in his first professional match.

  这位新秀在职业首秀中表现出色。

Act, behave, and acquit all mean to do something in a certain way, but formality differs. Act is common and neutral. Behave means following proper, polite conduct, often said of children. Acquit is formal, almost always used with an adverb, as in a hard test.

这三个词都表示“以某种方式行事、表现”，但正式程度和语气不同：act 最常用、最中性；behave 强调举止得体、合乎规矩；acquit oneself 较正式，多与反身代词和副词连用，指在考验或挑战中的表现。这里不比较 act 的“表演”义，也不比较 acquit 更常见的法律义“宣判无罪”。

Compared meaning: to pretend, to appear as something untrue (verb).

比较义项：假装、伪装成某种样子（动词）。

• pretend

  The general, everyday word for consciously behaving as if something untrue were true; commonly followed by 'that' or 'to be', often describing children's play or deliberate deception.

  最常用、最通用的词，表示故意表现得好像不真实的事是真的；常接 that 从句或 to be，多用于描述儿童游戏或蓄意欺骗。

  The twins pretended they were asleep when their mother checked on them.

  妈妈来查看时，这对双胞胎假装自己已经睡着了。

• act 本词

  Often paired directly with an adjective or 'as if' to describe faking an emotion or reaction; sounds slightly more formal or performance-like than 'pretend', and does not normally take a 'that'-clause.

  常直接与形容词或 as if 连用，表示假装出某种情绪或反应；语气比 pretend 稍正式，带有表演意味，通常不直接接 that 从句。

  She acted surprised, even though she already knew about the party.

  她其实早就知道派对的事，却还是装出很惊讶的样子。

Pretend and act both mean to fake something, but they differ. Pretend is common, often followed by 'that' or 'to be', used in games or deception. Act often pairs with an adjective or 'as if', and sounds more formal. Act's other sense is not compared.

这两个词在“假装”这一义项上意思相近，但用法不同：pretend 是最常用、最通用的说法，常接 that 从句或 to be，多用于儿童游戏或故意欺骗；act 常与形容词或 as if 连用，表示装出某种情绪或反应，语气稍显正式、带表演意味，一般不直接接 that 从句。这里不比较 act 表示“行动、办事”的义项（如 He had to act quickly during the emergency）。

Compared meaning: something a person does; an action (noun).

比较义项：行为，所做的事（名词）。

• act 本词

  General, neutral word for a single action; often paired with 'an act of' plus a quality such as kindness or violence; the action can be minor or major; act can also be used as a verb, unlike deed.

  泛指某个行为或举动，语气中性，常表示某种性质的行为，例如善举、暴行等，行为可大可小；act还可以作动词，而deed没有动词用法。

  Helping the lost tourist find his way was a simple act of kindness.

  帮助迷路的游客找路是一件简单的善举。

• deed

  Notable action, often admirable or heroic; more formal or literary in tone; common in fixed phrases like 'a good deed' or 'a heroic deed'; deed has no verb use.

  指值得注意的行为，往往含有英勇或高尚的意味，语体较正式或书面化，常出现在善举、英勇事迹等固定搭配中；deed没有动词用法。

  Rescuing the child from the river was a truly heroic deed.

  把孩子从河里救出来是一件真正英勇的行为。

Act and deed both mean an action a person does, but deed is more formal and literary, often describing an admirable or heroic action. Act is neutral and common, used with 'an act of' plus a quality like kindness. Deed has no verb use.

这两个词在表示某人所做的行为这一意义上很接近，但deed语气更正式、书面，多指值得称道或英勇的行为；act更中性、口语化，行为可大可小。这里不比较act作动词表示行动、表演的意思，也不比较deed表示契约、地契的意思。