noun

radian

RAY-dee-uhn

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Radian (noun) means In the International System of Units, the derived unit of plane angle, equal to the angle at the centre of a circle formed by an arc as long as the radius. Example: “A full circle measures roughly 6.28 radians.”

noun

geometry In the International System of Units, the derived unit of plane angle, equal to the angle at the centre of a circle formed by an arc as long as the radius.

"A full circle measures roughly 6.28 radians."

"The formula converts degrees into radians before the calculation runs."

"Students are taught to work in radians once they start calculus."

How to use radian

Learner’s notes

In plain EnglishIt is the standard scientific unit for measuring an angle, based on the circle's radius rather than an arbitrary division into 360 parts.

When to use it

It belongs to formal mathematical and scientific writing rather than everyday conversation.

Memory tip

Remember that radian comes from radius, which is the clue to how the unit is defined.

Trace the full origin ↓

Common pairings

measured in radians convert to radians radians per second angle in radians

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C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

Test yourself on “radian” A quick quiz — meaning, synonyms & usage →

Fill the gap

Can you complete this real example?

A full circle measures roughly 6.28 _____.

Etymology

The word is formed from radius with the suffix -an added to it, reflecting how the unit is defined directly from a circle's radius.

Origin: English

Synonyms

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rad

Related words

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Rhymes for radian

Asian Fabian Indian Syrian simian median Italian Russian Persian Serbian Latvian Belgian

See all rhymes for radian →

Frequently asked questions

What is a radian in simple terms?

It is the unit for measuring angles based on the radius of a circle: one radian is the angle made at the centre when the arc length equals the radius.

What is the symbol for radian?

The unit can be written using the symbol rad, or sometimes the superscript c.

How is a radian different from a degree?

Both measure angles, but a radian is defined from the circle's own radius and arc length, while a degree divides a circle into 360 equal parts; the two units are used side by side depending on context.

What is the meaning of radian?

"radian" (noun) means in the International System of Units, the derived unit of plane angle, equal to the angle at the centre of a circle formed by an arc as long as the radius.

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