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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  

abbreviation

1. registered (trademark)

2. right

3. river

4. rouble

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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  

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. 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

Noun Inflected Forms

• R's
  plural
• Rs
  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

County, the Civilian Oversight Commission has said the March ruling, AB 847 and Measure R combine to affirm its subpoena powers.

From Los Angeles Times • Jun. 17, 2026

Some longtime observers of Saudi Arabia, such as Ellen R Wald, the author of Saudi, Inc., feel like they've seen it all before.

From BBC • May 25, 2026

R: I never, ever imagined that this could happen.

From Barron's • May 21, 2026

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

From Salon • Apr. 19, 2026

Next I see the G, R, and A. I say it: “Full...of...grass?”

From "The Truth as Told by Mason Buttle" by Leslie Connor