illegal

illegal — adjective

1. describing an action, object, or situation that the legal system of a country or

1.adjectiveB1
Definition

describing an action, object, or situation that the legal system of a country or region does not allow — for example, selling certain drugs, copying protected content, or entering a country without permission.

Example

The company paid a large fine for making illegal payments to government officials.

collocation: illegal payments

Bilal discovered that downloading music without the creator's permission is illegal in most countries.

predicative: is illegal

Common collocations
  • illegal drugs
  • illegal activity
  • illegal trade
  • illegal parking
  • illegal downloading
  • illegal immigrant
  • illegal payments
Synonyms
  • unlawful

    more formal; common in legal documents and court rulings

  • illicit

    adds a moral dimension of social disapproval beyond mere illegality

  • banned

    emphasizes a specific prohibition by an authority; can apply to non-legal rules too

Antonyms
  • legal

    permitted by law — the direct opposite

  • lawful

    formal equivalent of legal, common in legal writing

Grammar Patterns

illegal + noun

it is illegal to + infinitive

Usage Note

Frequently used before nouns such as 'drugs,' 'activity,' 'immigration,' 'trade,' and 'download.' Distinguish from 'illegible' (cannot be read) and 'illicit' (socially or morally disapproved but not always against the law).

Common Mistakes

He was arrested for an illegible activity.
He was arrested for an illegal activity.
'Illegible' means the writing is too unclear to read, not that something is against the law.
This drug is illicit but not illegal.
This drug is both illicit and illegal.
'Illicit' implies moral wrongness; something can be socially disapproved (illicit) yet still legal, but in most cases the two overlap.

2. describing a move, play, or action that goes against the official rulebook of a

2.adjectiveB1
Definition

describing a move, play, or action that goes against the official rulebook of a sporting competition — for example, a tackle in football that hits an opponent from behind, or a serve in tennis thrown instead of struck.

Example

The referee stopped the game after Yuki made an illegal tackle from behind.

collocation: illegal tackle

Using both hands to push an opponent while running is illegal in basketball.

predicative: is illegal in [sport]

Common collocations
  • illegal tackle
  • illegal move
  • illegal play
  • illegal block
  • illegal serve
  • illegal hit
Synonyms
  • against the rules

    everyday language; less formal and not specific to sports

  • forbidden

    stricter tone, implies a clear prohibition with possible penalty

  • not allowed

    simplest plain-English alternative

Antonyms
  • legal

    within the rules of the sport

  • allowed

    permitted by the rules

Grammar Patterns

illegal + noun (action)

be + illegal + in + sport

Usage Note

Common in team sports (football, basketball, hockey, rugby) and individual sports (tennis, boxing). What counts as illegal varies by sport — always check the specific rulebook. Not used for mere bad sportsmanship that is not in the written rules.

Common Mistakes

The football player made an unlawful tackle.
The football player made an illegal tackle.
In sports contexts, 'illegal' is the standard term; 'unlawful' is reserved for the legal system.

illegal — noun

Word family

  • illegally
    adverbB1
  • illegality
    nounC1
  • legal
    adjectiveA2
  • legalize
    verbB2
  • legalization
    nounC1
  • legality
    nounC1

Synonym discussion

Sense: adjective/1

Illegal is the most general and frequent term for anything the law prohibits, from minor offences like illegal parking to serious crimes. Unlawful is more formal and appears often in legal texts and court rulings, carrying a sense of violating established legal principles. Illicit adds a moral dimension — it suggests that the activity is both against the law and socially disapproved of, as in illicit drugs or an illicit relationship. Criminal applies specifically to acts classified as crimes, which is a narrower set: an illegal act such as a parking violation is not criminal, whereas selling illicit drugs is both. For example, 'He made an illegal U-turn' describes a traffic infraction, while 'He was involved in illicit drug trafficking' describes a serious criminal offence.

illegal ↗unlawful ↗illicitcriminal ↗

Common collocations

Phrases

  • it is illegal to
  • declare something illegal
  • rule something illegal

Etymology

LatinFrenchEnglish

Illegal was formed in English around the 1620s by adding the negative prefix 'il-' (a variant of 'in-') to the word 'legal', which comes from Latin 'legalis' meaning 'pertaining to the law'. The Latin root 'lex' ('law') also gives us 'legislation', 'legitimate', and 'privilege'. Before 'illegal' became standard, English speakers used 'unlawful', which remains in use today as a more formal synonym.