What does "illegal" mean?

1. (against the law) not allowed by the law. 2. (against the rules) not allowed by the rules of a game or organization. 3. (person without papers) a person who lives or works in a country without the correct legal documents. 4. (undercover spy) a spy who works in a foreign country without any official connection to their own government.

How do you use "illegal"?

Commonly used as an attributive adjective before a noun or as a predicative adjective after a linking verb.

illegal

adj. · n.

US //ˌɪˈɫiɡəɫ// UK //ɪlˈiːɡəl// il·le·gal

1 against the law (adj.)
B1 Intermediate Law

not allowed by the law.

contrary to, forbidden by, or not authorised by law, particularly criminal or civil statutes.

Example

It is illegal to drive a car without a valid license.

Example

The company faced severe penalties after an investigation revealed they had been engaging in illegal dumping of toxic waste for years.

Usage

Commonly used as an attributive adjective before a noun or as a predicative adjective after a linking verb.
2 against the rules (adj.)
B2 Upper Intermediate Sport

not allowed by the rules of a game or organization.

forbidden by established rules or regulations within a specific non-legal context, such as sports or corporate policy.

Example

The referee called a foul because the player made an illegal move.

Example

The athlete was disqualified for using an illegal substance that was strictly prohibited by the international sporting federation.
- legal
- permitted

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3 person without papers (n.)
C1 Advanced Informal American English

a person who lives or works in a country without the correct legal documents.

an individual residing in a country without official legal authorization or valid immigration documents.

Example

The news report discussed the challenges faced by illegals living in the city.

Example

The documentary explores the precarious lives of illegals who work in the agricultural sector without any social protections.

Teacher's tip

This noun use is considered offensive by many people; 'undocumented immigrant' is the preferred neutral term in professional and academic contexts.
- undocumented immigrant
4 undercover spy (n.)
C2 Proficiency Technical Formal

a spy who works in a foreign country without any official connection to their own government.

an intelligence officer operating under deep cover in a foreign country without diplomatic immunity or official ties to their home state.

Example

The agency spent years training the illegal to blend into the local community.

Example

The exchange of captured illegals took place on a bridge at midnight, following months of quiet diplomatic negotiations between the two rival nations.
- sleeper agent
- deep cover agent

Origin

Borrowed from French illégal, from Medieval Latin illegalis, from Latin legalis, by surface analysis, il- + legal. In senses relating to immigration, via clipping of illegal alien or illegal immigrant.