act up
B1 (Intermediate)Informal
Definition
Meaning
to behave badly or dysfunctionally
Used to describe people (especially children) misbehaving, or objects/body parts malfunctioning or causing trouble.
Linguistics
Semantic Notes
Always intransitive, phrasal verb. The 'up' particle adds a sense of intensification or problematic emergence.
Dialectal Variation
British vs American Usage
Differences
Minimal. Slightly more common in American English for describing malfunctioning technology.
Connotations
Informal, often with a tone of mild frustration or annoyance rather than serious anger.
Frequency
Common in both varieties.
Vocabulary
Collocations
Grammar
Valency Patterns
SUBJ + act up (where SUBJ is a person or thing)Vocabulary
Synonyms
Strong
Neutral
Weak
Vocabulary
Antonyms
Phrases
Idioms & Phrases
- “[Not typically part of larger idioms]”
Usage
Context Usage
Business
Rare, except informally: 'The server is acting up again.'
Academic
Very rare.
Everyday
Very common for discussing children's behaviour or minor technical/health issues.
Technical
Informal use in IT/mechanics: 'The software module has been acting up since the update.'
Examples
By Part of Speech
verb
British English
- The children always act up when they're tired.
- My back has been acting up in this damp weather.
American English
- The photocopier is acting up again.
- He tends to act up when there's a substitute teacher.
Examples
By CEFR Level
- The baby acts up if her nap is late.
- My laptop started acting up, so I saved my work immediately.
- The negotiations were proceeding smoothly until one delegate decided to act up and derail the talks.
- Aware that the cameras were on him, the protester began to act up more flamboyantly to ensure his message was seen.
Learning
Memory Aids
Mnemonic
Imagine a child actor (ACT) on a stage, suddenly standing UP and throwing a tantrum – they are ACTing UP.
Conceptual Metaphor
PROBLEMATIC BEHAVIOR IS REBELLIOUS PERFORMANCE (the entity 'acts' in a disruptive way).
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Do not translate literally as 'действовать вверх'. The phrase is idiomatic for 'безобразничать' (people) or 'глючить/сбоить' (technology/body).
Common Mistakes
- Using it transitively (e.g., 'He acted up the class' is wrong). Confusing it with 'act out' (which more specifically means to express emotions through behaviour, often in psychology).
Practice
Quiz
In which scenario is 'act up' LEAST appropriate?
FAQ
Frequently Asked Questions
'Act up' means to misbehave or malfunction. 'Act out' means to express unconscious emotions through behaviour or to perform a scenario (e.g., act out a play). 'Act out' can also mean to behave rebelliously, but with a stronger focus on expressing internal conflict.
Typically not. It suggests annoying, troublesome, or inconvenient behaviour/malfunctions, not serious crime or violence. It's often used for minor, recurrent issues.
Yes, very commonly. It's a versatile informal term for any entity (person, machine, body part) that is not functioning as it should in a troublesome way.
Not in standard use. The noun forms would be 'misbehaviour' or 'malfunction'.