Definition

1. Verb (transitive or intransitive):
   • To function in the capacity of; to serve as. This meaning describes something or someone performing the role, duties, or function of something else, often temporarily or in a specific context.
   • To pretend to be; to behave in a manner characteristic of. This meaning describes consciously adopting a specific quality, emotion, or state of mind, often for a purpose.

Usage Examples

• Functioning as something:

  • During the emergency, the senior nurse had to act as the head of the department.
  • A thick book can act as a paperweight.
  • This committee will act as an advisory board for the project.

• Pretending to have a quality:

  • He acted as if he knew nothing about the surprise party.
  • She often acts as the expert, even when she's unsure.
  • You don't have to act as the tough guy all the time.

Advanced Usage

• "act as a go-between": to serve as an intermediary or messenger between two parties.

  • My colleague acted as a go-between during the sensitive negotiations.

• "act as a catalyst": to serve as the agent that precipitates a process or event.

  • The scandal acted as a catalyst for major political reform.

Variants and Related Words

• Act (verb): To perform a role; to behave in a specified way.
  • He will act in the new film.
• Serve as (verb phrase): A close synonym for the "function as" meaning of "act as".
  • This room serves as our office.

Synonyms

• Function as: To operate or work as.
• Serve as: To perform the duties of.
• Pose as: To pretend to be (often with deceptive intent).
• Feign: To pretend to be affected by (a feeling, state, or injury).

Related Phrasal Verbs / Constructions

• Act up: To misbehave or function improperly.
  • The old computer started to act up again.
• Act on/upon: To take action as a result of something.
  • The police must act on the information they receive.
• Act out: To express emotions or conflicts through behavior, often unconsciously; to perform a scene or story.
  • Children sometimes act out when they are tired.

Related Idioms

• Act one's age: To behave in a manner appropriate to one's maturity level.
  • He's thirty but still doesn't act his age.
• Act the fool / act the part: To behave foolishly or to behave in a way that fits a particular role.
  • Stop acting the fool and be serious for a moment.

Verb

1. pretend to have certain qualities or state of mind
   • He acted the idiot
   • She plays deaf when the news are bad
2. function as or act like
   • This heap of stones will act as a barrier