informal

informal — adjective

1. Done without following official rules, formal procedures, or accepted customs —

1.adjectiveB1
Definition

Done without following official rules, formal procedures, or accepted customs — for example, an informal agreement between friends that is not written down.

Example

Anjali and Ignacio made an informal agreement to share taxi rides to work.

collocation: informal agreement

Ryo's promotion was discussed informally over lunch rather than in a proper meeting.

Common collocations
  • informal agreement
  • informal meeting
  • informal arrangement
  • informal discussion
  • informal system
  • informal gathering
Synonyms
  • unofficial

    Focuses on lack of official recognition; 'unofficial' is often used for rules or reports, while 'informal' is broader.

  • off-the-record

    More specific — describes information not meant to be made public or attributed.

  • unceremonious

    Describes actions done without the expected formalities; slightly more literary.

Antonyms
  • official

    The direct opposite; 'official' things follow established rules or procedures.

  • formal

    The broader opposite across both senses; formal events follow strict customs and protocols.

Grammar Patterns

informal + noun

be + informal

Usage Note

This sense is frequently used to describe arrangements, systems, or meetings that lack official status or documentation. The opposite is formal.

Common Mistakes

The meeting was informal, so I had to fill out many forms.
The meeting was informal, so no official forms were needed.
'informal' means few or no official procedures, not the opposite.
He made an informal speech to the president at the state dinner.
He made an informal speech to his team during the company picnic.
'informal' describes relaxed settings; formal events call for formal behaviour.

2. (Of clothes, language, or behaviour) relaxed and suitable for everyday situation

2.adjectiveB1
Definition

(Of clothes, language, or behaviour) relaxed and suitable for everyday situations with people you know, rather than for official or serious events.

Example

For the beach party, Nicholas wore informal clothes like shorts and a simple T-shirt.

collocation: informal clothes

The professor prefers an informal style where students call him by his first name.

collocation: informal style

Common collocations
  • informal clothes
  • informal language
  • informal style
  • informal atmosphere
  • informal setting
  • informal gathering
  • informal tone
Synonyms
  • casual

    Almost interchangeable for clothing and behaviour; 'casual' is slightly more common for describing dress codes.

  • relaxed

    Focuses on the comfortable, unhurried feeling rather than the absence of rules.

  • friendly

    Describes the warm, welcoming quality of an informal situation between people.

Antonyms
  • formal

    The direct opposite — formal dress, language, or behaviour follows strict rules for official occasions.

  • dressy

    Specifically for clothing; dressy clothes are elegant and suitable for special events.

  • stiff

    Describes behaviour or atmosphere that is overly formal and lacking in warmth.

Grammar Patterns

informal + noun

be + informal

Usage Note

Commonly appears with nouns describing clothing (informal clothes, informal dress), communication (informal language, informal tone), and settings (informal atmosphere, informal gathering). This sense contrasts with formal and does not imply poor quality or lack of respect.

Common Mistakes

He speaks informal English, which means his grammar is always wrong.
He speaks informal English, meaning he uses casual expressions suitable for talking to friends.
'informal' language is not incorrect; it just follows different conventions from formal language.
She wore informal dress to the job interview.
She wore formal business attire to the job interview.
Job interviews are official occasions that usually require formal or at least smart-casual clothing, not informal dress.

Word family

  • informality
    nounB2
  • informally
    adverbB1
  • formal
    adjectiveB1
  • formality
    nounB2
  • formally
    adverbB1

Synonym discussion

Sense: adjective/2

All four words describe situations that are not stiff or official, but they differ in focus. 'Casual' is the closest synonym to 'informal' and is most common for dress codes and social gatherings — a casual Friday dress policy is exactly an informal one. 'Relaxed' emphasises the comfortable, unhurried feeling of a situation rather than the absence of rules; a relaxed conversation feels easy-going even in a formal setting. 'Friendly' highlights warmth and personal connection — a friendly tone in an email makes the reader feel welcomed, whereas an informal tone might just avoid strict conventions. 'Informal' itself is the broadest term, covering everything from language ('informal expressions') to behaviour ('informal manners'). In practice: 'The party had a relaxed, friendly atmosphere where casual clothes were fine' is a typical native sentence that uses all three near-synonyms together.

casual ↗relaxed ↗friendly ↗informal ↗

Common collocations

Nouns

Adverbs

  • quite informal
  • very informal
  • rather informal
  • fairly informal

Phrases

  • informal in nature
  • on an informal basis

Prepositions

  • informal with
  • informal about

Etymology

LatinFrenchEnglish

The word 'informal' comes from Latin 'informalis', meaning 'not according to form'. It was formed by adding the prefix 'in-' (meaning 'not') to 'formalis' (meaning 'relating to form or official procedure'). The word entered English in the mid-15th century and originally meant 'not in proper form'. By the 17th century it had developed its modern meanings of 'unofficial' and 'casual'.