R, r

WordReference Random House Learner's Dictionary of American English © 2025

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 © 2025

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.