radar

radar — noun

1. a system that works by sending out high-frequency radio waves and reading their

1.nounB2
Definition

a system that works by sending out high-frequency radio waves and reading their reflected signals, making it possible to locate far-away things like planes, boats, or approaching storms

Example

Hassan spotted a small plane on his radar screen before anyone else did.

collocation: radar screen

Police set up a radar trap and caught several cars going too fast.

collocation: radar trap

Common collocations
  • radar screen
  • radar system
  • radar detector
  • radar gun
  • radar trap
  • weather radar
  • police radar
  • on radar
  • appear on radar
  • track by radar
Synonyms
  • radio detection and ranging

    the full expanded acronym; highly technical, rarely used in everyday speech

  • sonar

    uses sound waves instead of radio waves; used underwater rather than through air

  • lidar

    uses laser light pulses instead of radio waves; used for high-resolution mapping

Grammar Patterns

radar + noun (radar screen, radar system)

adjective + radar (weather radar, police radar)

on radar

Usage Note

Radar is most often uncountable — we say 'the plane appeared on radar' not 'on a radar'. When countable, it refers to a specific type or instance: 'The navy installed three new radars on the base.' The noun is frequently used attributively before another noun (radar screen, radar gun, radar signal).

Common Mistakes

The air traffic controller looked at a radar.
The air traffic controller looked at the radar screen.
Radar is typically uncountable; use 'radar screen' or 'radar system' when referring to the display or equipment.
The radar showed a storm.
The weather radar showed a storm approaching.
Adding 'weather' or 'police' before 'radar' specifies the type of system being used.

2. the state of being seen, noticed, or considered by the public or by a particular

2.nounB2
Definition

the state of being seen, noticed, or considered by the public or by a particular person or group, used mainly in fixed phrases about receiving or avoiding attention — for example, keeping an activity under the radar to avoid detection, or having an issue come onto a decision-maker's radar

Example

That new restaurant is not on my radar yet, but a friend recommended the pasta there.

idiom: not on [possessive] radar

The small startup stayed under the radar for three years before becoming a well-known brand.

idiom: under the radar

Common collocations
  • on my radar
  • on the radar of
  • under the radar
  • off the radar
  • fall off the radar
  • come onto the radar
  • stay under the radar
  • not on the radar
Synonyms
  • attention

    broader and less colourful; lack the metaphor of detection from a distance

  • awareness

    similar but less vivid; 'public awareness' is more formal than 'on the public radar'

  • notice

    implies a brief or surface-level observation rather than focused attention

Antonyms
  • obscurity

    the state of being unknown or unnoticed; more formal and less vivid than the radar metaphor

Grammar Patterns

on [possessive] radar

under the radar

off [possessive] radar

come onto [possessive] radar

Usage Note

This is an extended metaphorical sense of the original radar meaning. The phrase 'under the radar' generally has a positive or neutral connotation when describing clever avoidance; 'on someone's radar' can be neutral or slightly urgent. 'Off the radar' is typically neutral, describing something simply not receiving attention. Unlike sense 1, this sense cannot be used with a countable form or in technical compound nouns.

Common Mistakes

The issue is on radar.
The issue is on my radar.' or 'The issue is on the radar of the committee.
The metaphorical sense requires a possessive or 'the' before 'radar'; bare 'on radar' is only used in the technical sense.
He wants to stay under a radar.
He wants to stay under the radar.
Always use the definite article 'the' in this fixed phrase.
Idioms

on someone's radar

idiom

being noticed, considered, or thought about by a particular person or group

Lan put studying abroad on her radar after talking to a friend who studied in Canada.

The issue of plastic waste was not on the government's radar until the protests began.

under the radar

idiom

happening or existing without being noticed by the public or by those in charge

The band released four albums under the radar before finally becoming famous.

Shanti managed to slip under the radar during the meeting so nobody asked her any questions.

off someone's radar / fall off the radar

idiom

no longer being noticed, considered, or remembered by a person or group

After she left the company, she completely fell off everyone's radar in the industry.

Eitan's idea was interesting at first but quickly fell off the radar when the budget was cut.

below/under the radar

idiom

This means that something is not noticed or known by most people.

Maya's small business stayed under the radar for years.

Did the error slip below the radar during the review?

on/off the radar (screen)

idiom

This means that something is either receiving attention or not being noticed anymore.

Climate change is back on the radar after the summit.

The old scandal has completely fallen off the radar screen.

Word family

  • radar detector
    nounB2
  • radar gun
    nounB2

Synonym discussion

Sense: noun/1

Radar, sonar, and lidar are all detection technologies that locate objects by sending out signals and reading the reflected returns, but they use different types of waves for different environments. Radar uses radio waves through air and is the most common term in everyday language — found in weather reports, air traffic control, and police enforcement. Sonar (SOund Navigation And Ranging) uses sound waves underwater, so you talk about a submarine's sonar, not its radar. Lidar (Light Detection And Ranging) uses laser pulses for extremely high-resolution scanning, commonly used in self-driving cars and archaeology. A 'detection system' is a broader, non-specific term that could describe any of these technologies or a simpler alarm-based system. In everyday English: a pilot uses radar to navigate through clouds; a ship uses sonar to map the ocean floor; a self-driving car uses lidar to see the road ahead.

radar ↗sonarlidardetection system

Common collocations

Nouns

Adverbs

  • on — appear on radar, show up on radar
  • under — stay under the radar, fly under the radar

Phrases

  • radar screen
  • radar system
  • radar detector
  • radar gun
  • radar trap
  • radar signal
  • radar image

Prepositions

  • by — track by radar, detect by radar
  • on — on radar, on the radar screen

Etymology

English (acronym)

Radar is an acronym formed during World War II from 'RAdio Detection And Ranging'. The term was coined by the United States Navy in 1940 as a code name for secret detection technology and quickly became a common noun in English. The underlying technology was developed independently by several countries (the US, Britain, Germany, France, and Japan) in the 1930s, using radio waves from early transmitters to detect approaching aircraft. By the end of the war, radar was a household word, and its metaphorical use — referring to the range of someone's attention or awareness — emerged in the mid-20th century.