R

UK: 'R', 'r': /ˈɑː^r/ US: 'R', 'r': /ɑr/ ,'R', 'r': (är)

Collins Concise English Dictionary © HarperCollins Publishers::

R symbol

1. radical
2. rand
3. rupee
4. Réaumur temperature (scale)
5. reproduction or reproductive (indicating the expected number of people who will catch a disease from a single infected person)
6. resistance
7. roentgen or röntgen
8. rook
9. Royal
10. gas constant
11. (in the US and Australia) restricted exhibition (used to describe a category of film certified as unsuitable for viewing by anyone under the age of 18)
12. (as modifier): an R film

WordReference Random House Learner's Dictionary of American English © 2026

R, r /ɑr/   n., pl. Rs or R's, rs or r's. 

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

R,  an abbreviation of:

1. Mathematics ratio.
2. Biochemistry, Clothing regular: a man's suit or coat size.
3. Show Business restricted: a motion-picture rating advising that children under the age of 17 will not be admitted unless accompanied by an adult. Compare G (def. 2),NC-17,PG,PG-13,X (def. 7).
4. Show Business right.

R,  [Symbol.]

1. registered trademark: written as superscript ® following a name registered with the U.S. Patent and Trademark Office.
2. Electronics resistance.

r,  an abbreviation of:

1. radius.

R.,  an abbreviation of:

1. Mathematics radius.
2. Rail Transport railroad.
3. Rail Transport railway.
4. Government Republican.
5. right.
6. river.
7. road.

r.,  an abbreviation of:

1. Rail Transport railroad.
2. Rail Transport railway.
3. right.
4. river.
5. road.
6. Weights and Measures rod.

WordReference Random House Unabridged Dictionary of American English © 2026

R, r  (är), n., pl. R's or Rs, r's or rs. 

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 ofR.
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. See three R's. 

R  (är), 

1. Informal Terms v. are:
   Oysters R in season.

R, 

1. Chemistry radical.
2. Mathematics ratio.
3. Biochemistry, Clothing regular: a man's suit or coat size.
4. Electricity resistance.
5. Show Business restricted: a rating assigned to a motion picture by the Motion Picture Association of America indicating that children under the age of 17 will not be admitted unless accompanied by an adult. Cf. G (def. 7), PG, PG–13, X. [abbrev. for restricted]
6. Show Business [Theat.] stage right.
7. Physics roentgen.
8. Chess rook.

R,  Symbol.

1. the 18th in order or in a series, or, when I is omitted, the 17th.
2. (sometimes l.c.) the medieval Roman numeral for 80. Cf. Roman numerals. 
3. Biochemistry arginine.
4. [Physics.] See universal gas constant. 
5. registered trademark: written as superscript ® following a name registered with the U.S. Patent and Trademark Office.

r, 

1. radius.
2. Business [Com.] registered (def. 2).
3. [Elect.] resistance.
4. Physics roentgen.
5. royal.
6. Currency ruble.
7. Currency pl. rs, rupee.

r, [Ecol.]

1. Ecology 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. Also called Malthusian parameter. 

R., 

1. Judaism rabbi.
2. Radical.
3. Mathematics radius.
4. Rail Transport railroad.
5. Rail Transport railway.
6. Currency (in South Africa) rand;
   rands.
7. Réaumur.
8. Drugs Also, R (in prescriptions) take.
• Latin recipe
9. rector.
10. redactor.
11. regina.
12. Government Republican.
13. response.
14. rex.
15. river.
16. road.
17. royal.
18. Currency ruble.
19. Currency rupee.
20. Show Business [Theat.] stage right.

r., 

1. rabbi.
2. Rail Transport railroad.
3. Rail Transport railway.
4. range.
5. rare.
6. [Com.] received.
7. recipe.
8. replacing.
9. residence.
10. right.
11. rises.
12. river.
13. road.
14. Weights and Measures rod.
15. royal.
16. rubber.
17. Currency ruble.
18. Sport [Baseball.] run;
    runs.
19. Currency pl. rs. rupee.

Collins Concise English Dictionary © HarperCollins Publishers::

r, R / ɑː/ noun (r's, R's, Rs)

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

Collins Concise English Dictionary © HarperCollins Publishers::

R., r. abbreviation

1. registered (trademark)
2. right
3. river
4. rouble

R. abbreviation

1. rabbi
2. rector
3. Regina
4. Republican
5. response (in Christian liturgy)
6. Rex
7. River
8. Royal

Etymology: (for sense 3) Latin: Queen; (for sense 6) Latin: King

Collins Concise English Dictionary © HarperCollins Publishers::

r. abbreviation

1. rare
2. recto
3. Also: r rod (unit of length)
4. ruled
5. run(s)