R 1 (är) A trademark for a movie rating indicating that admission will be granted only to persons of or over a certain age, usually 17, unless accompanied by a parent or guardian.R 21. The symbol for gas constant.2. The symbol for a hydrocarbon side chain or substituent of variable chemical structure.R 3abbr.1. range (surveying)2. Réaumur (scale)3. registered trademark4. Republican5. Ecclesiastical response6. right7. or r roentgen8. rook (chess)9. Baseball runr 1 or R (är)n. pl. r’s or R’s also rs or Rs 1. The 18th letter of the modern English alphabet.2. Any of the speech sounds represented by the letter r.3. The 18th in a series.4. Something shaped like the letter R.r 2abbr.1. Mathematics radius2. Genetics recombinant3. or R Electricity resistanceAmerican Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.r (??) or Rn, pl r’s, R’s or Rs1. (Linguistics) the 18th letter and 14th consonant of the modern English alphabet2. (Phonetics & Phonology) a speech sound represented by this letter, in English usually an alveolar semivowel, as in red3. (Education) See three RsR symbol for 1. (Chemistry) chem radical 2. (Currencies) currency a. randb. rupee 3. (General Physics) Réaumur temperature (scale) 4. (General Physics) physics electronics resistance 5. (General Physics) roentgen or röntgen 6. (Chess & Draughts) chess rook 7. Royal 8. (Chemistry) chem gas constant 9. (Film) (in the US and Australia)a. restricted exhibition (used to describe a category of film certified as unsuitable for viewing by anyone under the age of 18)b. (as modifier): an R film. Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014R, r (?r) n., pl. Rs R’s, rs r’s. 1. the 18th letter of the English alphabet, a consonant. 2. any spoken sound represented by this letter. 3. something shaped like an R. 4. a written or printed representation of the letter R or r. R 1. Chem. radical. 2. Math. ratio. 3. regular: a man’s suit or coat size. 4. restricted: a motion-picture rating advising that children under 17 will not be admitted unless accompanied by an adult. Compare G (def. 2), NC-17, PG, PG-13, X (def. 7). 5. right. 6. roentgen. R Symbol. 1. the 18th in order or in a series. 2. arginine. 3. registered trademark: written as superscript ® following a name registered with the U.S. Patent and Trademark Office. 4. Elect. resistance. r 1. radius. 2. Elect. resistance. 3. roentgen. 4. royal. 5. ruble. 6. pl. rs, rupee. r Ecol. the 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. rabbi. 2. Radical. 3. radius. 4. railroad. 5. railway. 6. (in South Africa) rand. 7. Réaumur. 8. Also, R (in prescriptions) take. [