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• r
  r

  the theoretical intrinsic rate of increase of a population, equivalent to the difference between the birth and death rates divided by the number of individuals in the population.
• R
  R

  noun

  the 18th letter of the English alphabet, a consonant.
• r.
  r.

  abbreviation

  rabbi.
• R.
  R.

  abbreviation

  (in prescriptions) take.

r

¹ American  

Ecology.

1. the theoretical intrinsic rate of increase of a population, equivalent to the difference between the birth and death rates divided by the number of individuals in the population.

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r ² American  

abbreviation

rs plural

1. radius.

2. Commerce. registered.

3. Electricity. resistance.

4. Physics. roentgen.

5. royal.

6. ruble.

7. rupee.

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R ³ American  

[ahr] / ɑr /

Or r

noun

R's, plural Rs, plural r's, plural rs plural

1. the 18th letter of the English alphabet, a consonant.

2. any spoken sound represented by the letter R or r, as in ran, carrot, or rhyme.

3. something having the shape of R .

4. a written or printed representation of the letter R or r.

5. a device, as a printer's type, for reproducing the letter R or r.

6. three R's.

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R ⁴ American  

[ahr] / ɑr /

verb

1. Informal. are.

   Oysters R in season.

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R ⁵ American  

abbreviation

1. Trademark. restricted: a rating assigned to a movie by the MPA indicating that children under the age of 17 will not be admitted to a theater showing the film unless accompanied by an adult.

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R ⁶ American  

abbreviation

1. Chemistry. radical.

2. Mathematics. ratio.

3. regular: a man's suit or coat size.

4. Electricity. resistance.

5. Theater. stage right.

6. Physics. roentgen.

7. Chess. rook.

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R ⁷ American  

Symbol.

1. the 18th in order or in a series.

2. (sometimes lowercase) the medieval Roman numeral for 80.

3. Biochemistry. arginine.

4. Physics. universal gas constant.

5. registered trademark: written as superscript ® following a name registered with the U.S. Patent and Trademark Office.

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r. ⁸ American  

abbreviation

rs plural

1. rabbi.

2. railroad.

3. railway.

4. range.

5. rare.

6. Commerce. received.

7. recipe.

8. replacing.

9. residence.

10. right.

11. rises.

12. river.

13. road.

14. rod.

15. royal.

16. rubber.

17. ruble.

18. Baseball. run; runs.

19. rupee.

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R. ⁹ American  

Or R.

abbreviation

1. (in prescriptions) take.

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R. ¹⁰ American  

abbreviation

1. rabbi.

2. Radical.

3. radius.

4. railroad.

5. railway.

6. (in South Africa) rand; rands.

7. Réaumur.

8. rector.

9. redactor.

10. regina.

11. Republican.

12. response.

13. rex.

14. river.

15. road.

16. royal.

17. ruble.

18. rupee.

19. Theater. stage right.

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R ¹ British  

symbol

1. chem radical

2. currency

   1. rand

   2. rupee

3. Réaumur temperature (scale)

4. physics electronics resistance

5. roentgen or röntgen

6. chess rook

7. Royal

8. chem gas constant

9. 1. restricted exhibition (used to describe a category of film certified as unsuitable for viewing by anyone under the age of 18)

   2. ( as modifier )

      an R film

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R. ² British  

abbreviation

1. rabbi

2. rector

3. Regina

4. Republican

5. response (in Christian liturgy)

6. Rex

7. River

8. Royal

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R. ³ British  

abbreviation

1. registered (trademark)

2. right

3. river

4. rouble

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r. ⁴ British  

abbreviation

1. rare

2. recto

3. Also: r.  rod (unit of length)

4. ruled

5. cricket baseball run(s)

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r ⁵ British  

/ ɑː /

noun

1. the 18th letter and 14th consonant of the modern English alphabet

2. a speech sound represented by this letter, in English usually an alveolar semivowel, as in red

3. See three Rs

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r Scientific  

1. Abbreviation of radius

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R Idioms  

1. see three R's.

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Other Word Forms

Inflected Forms

noun

• rs
  plural
• r's
  plural
• R's
  plural
• Rs
  plural

Etymology

Origin of R⁵

An American designation established in 1968

Origin of R.⁹

From the Latin word recipe

Example Sentences

The woman and her partner, identified by authorities as Marine R and Marc B, were arrested in Fatima on Thursday.

From BBC • May 23, 2026

“It hasn’t mattered if there was an R or a D after their name,” Roxanne said.

From Salon • Apr. 19, 2026

“L.A. County voters overwhelmingly approved Measure R in March 2020 to grant the Commission subpoena powers,” the Civilian Oversight Commission wrote in a statement.

From Los Angeles Times • Apr. 1, 2026

"During its visit the USS Gerald R Ford will host local officials and key leaders to recognise the strong and enduring alliance between the United States and Croatia," the embassy statement said.

From Barron's • Mar. 28, 2026

To my surprise, he was back a couple of hours later when the R side returned from lunch.

From "Newjack: Guarding Sing Sing" by Ted Conover