Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The 18th letter of the modern English alphabet.
  • n. Any of the speech sounds represented by the letter r.
  • n. The 18th in a series.
  • n. Something shaped like the letter R.
  • abbr. radius
  • abbr. Electricity resistance

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The eighteenth letter of the basic modern Latin alphabet.
  • n. radius
  • n. alveolar trill
  • n. used in several romanization systems of non-Latin scripts to represent an various other rhotic sounds (IPA: /r/).
  • n. The eighteenth letter of the English alphabet, called ar and written in the Latin script.
  • n. The ordinal number eighteenth, derived from this letter of the English alphabet, called ar and written in the Latin script.
  • v. are (in text messaging and internet conversations)

from the GNU version of the Collaborative International Dictionary of English

  • R, the eighteenth letter of the English alphabet, is a vocal consonant. It is sometimes called a semivowel, and a liquid. See Guide to Pronunciation, §§ 178, 179, and 250-254.

from The Century Dictionary and Cyclopedia

  • The eighteenth letter and fourteenth consonant in the English alphabet, representing a character having a like position and value in the alphabets from which the English is derived—the Latin, Greek, and Phenician.
  • The tag below the curve by which the English (and the Latin) R differs from the later (Greek form P was added to the latter in order to distinguish it from the p-sign after this had assumed its present form; the addition was first made on Greek ground, but was abandoned there when the distinction of the p- and r-signs had become established in another way. The value of the character has always been essentially the same; it represents a continuous sonant utterance made between the tip of the tongue and the roof of the mouth, at a point more or less removed backward from the upper front teeth. The sound is so resonant and continuable as to be nearly akin with the vowels; and it is, in fact, used as a vowel in certain languages, as Sanskrit and some of the Slavic dialects: in normal English pronunciation, however, it never has that value. By its mode of production it is nearly akin with l, and r and l are to a large extent interchangeable with one another in linguistic history. It is often classed as a “liquid,” along with l, m, n; less often, but more accurately, as a semivowel, with l, y, w. It also, on no small scale, answers as corresponding sonant (in languages that have no z) to s as surd, and comes from s under sonantizing influences: so in Sanskrit, in Latin (as ara from asa), and in Germanic (as in our were, plural of was). In Anglo-Saxon the initial r of many words was aspirated (that is, pronounced with an h before it), as hring (our ring); but the aspiration was long ago abandoned, both in pronunciation and in spelling. In Greek initial r was always thus aspirated, and the combination was transliterated in Latin by rh instead of hr: hence the frequency of rh iu our words of Greek derivation. Moreover, such an r, when by inflection or composition made medial, became rrh, and double r was in general viewed as rrh: whence that spelling in many of our words (for example, diarrhea, hemorrhage, catarrh, etc.): in recent scientific words and names taken from Greek, the Greek rule and Latin practice as regards the doubling and aspiration of the r are often neglected. The mode of production of the r-sound itself varies greatly in different languages and dialects. Normally its utterance is combined with a distinct trilling or vibration of the tip of the tongue, in various degrees (the sound is thence often called the “dog's letter,” littera canina). But in ordinary English pronunciation this vibration is either extremely slight, or, more commonly, altogether wanting; in fact, the tip of the tongue is drawn too far back into the dome of the palate to admit of vibration; the English r is a smooth r. But further, in many localities, even among the most cultivated speakers, no r is ever really pronounced at all unless followed (in the same word, or, if final, in the word following) by a vowel (for example, in are, farther, pronounced ah, father); it either simply disappears, or, as after most long vowels, is replaced by a bit of neutral-vowel sound, of ũ or é; and after such a long vowel, if it comes to be pronounced by the addition of a vowel, it retains the same neutral-vowel sound as transition-sound (for example, in faring, fearing, pouring, during, firing, souring: the pronunciation is indicated in this work by retaining the r in the same syllable with the long vowel: thus, fār′ ing, fēr′ tng, etc.). An r has a stronger and more frequent influence upon the character of the preceding vowel than any other consonant; hence the reduction to similarity of the vowel-sounds in such words as pert, dirt, curt, earn, myrrh. If all our r's that are written are pronounced, the sound is more common than any other in English utterance (over seven per cent.); the instances of occurrence before a vowel, and so of universal pronunciation, are only half as frequent. There are localities where the normal vibration of the tip of the tongue is replaced by one of the uvula, making a guttural trill, which is still more entitled to the name of “dog's letter” than is the ordinary r: such are considerable parts of France and Germany; the sound appears to occur only sporadically in English pronunciation.
  • As a medieval Roman numeral, 80, and with a line over it (), 80,000.
  • As an abbreviation:
  • Of Rex or Regina, as in George R., Victoria R.
  • Of Royal, as in R. N. for Royal Navy, R. A. for Royal Academy or Academician, or for Royal Arch (in freemasonry).
  • Prefixed to a medical prescription (℞), of recipe, take.
  • Nautical:
  • In a ship's log-book, of rain.
  • When placed against a man's name in the paymaster's book, of run away.
  • Of right (right-hand), as in R. A. for right ascension, R. H. E. for right second entrance (on the stage of a theater).
  • In math., r is generally a radius vector of coordinates, R the radius of a circle, ρ a radius of curvature.
  • An abbreviation of Royal Marines;
  • Royal Mail;
  • Resident Magistrate.
  • An abbreviation of Royal Navy.
  • An abbreviation of Radical;
  • of railway;
  • [lowercase] of rare;
  • [lowercase or cap.] of read;
  • of Réaumur (see thermometer);
  • of rector;
  • of Republican;
  • [lowercase] of residence and resides;
  • of response;
  • of the Latin Respublica, ‘the Republic’;
  • [lowercase or cap.] of retired;
  • of river;
  • [lowercase or cap.] of rod or rods;
  • of Roma, Rome;
  • [lowercase or cap.] of rood or roods;
  • [lowercase] in geometry, of radius (of the incircle); r1, r2, r3, denote the ex-radii beyond a, b, c, respectively; R denotes the radius of the circumcircle;
  • [capitalized] in psychophysics, an abbreviation of G. Reiz, stimulus.
  • As a symbol: In chem., R has been used for rhodium: more generally, Rh.
  • In elect., R or r denotes resistance.
  • In electrotechnics, r stands for radius.
  • An abbreviation of Receiving Office.
  • An abbreviation of Rifle Volunteers.
  • An abbreviation of railway. Also Rw.
  • n. An abbreviation of Royal Academy;
  • n. Royal Academician;
  • n. Royal Arch;
  • n. right ascension.
  • n. An abbreviation of Roman Catholic.
  • n. An abbreviation of Royal Dragoons;
  • n. of Rural Dean.
  • n. An abbreviation of Royal Engineers;
  • n. of Royal Exchange.
  • n. An abbreviation of Revised Version (of the Bible).
  • n. An abbreviation of Right Worshipful; Right Worthy.
  • n. An abbreviation of Rear-Admiral;
  • n. of Royal Arcanum;
  • n. of Royal Artillery (also R. Art.).
  • n. An abbreviation of Rifle Brigade.
  • n. An abbreviation of Red Cross
  • n. [lowercase] of right center.
  • n. In electrotherapy, an abbreviation of reaction of degeneration.
  • n. An abbreviation of Reformed Episcopal
  • n. of Right Excellent
  • n. [lowercase] of right eye.
  • n. An abbreviation of rapid fire;
  • n. in mineralogy, of reducing flame;
  • n. [capitalized] of République Française, French Republic;
  • n. [capitalized] of Rex Francorum, King of the Franks (French).
  • n. An abbreviation of right hand;
  • n. [capitalized] of Royal Highness.
  • n. An abbreviation of Rhode Island.
  • n. An abbreviation of Reformed Presbyterian
  • n. of Regius Professor
  • n. of the Latin Respublica, republic.
  • n. An abbreviation of railroad.
  • n. An abbreviation of Recording Secretary
  • n. of Revised Statutes
  • n. [lowercase] of right side
  • n. of Royal Society of London.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. (physics) the universal constant in the gas equation: pressure times volume = R times temperature; equal to 8.3143 joules per kelvin per mole
  • n. a unit of radiation exposure; the dose of ionizing radiation that will produce 1 electrostatic unit of electricity in 1 cc of dry air
  • n. the length of a line segment between the center and circumference of a circle or sphere
  • n. the 18th letter of the Roman alphabet

Etymologies

Modification of capital letter R by not closing the bottom of the loop but continuing into the leg to save a pen stroke, later shortening the right leg into a simple arc. (Wiktionary)
From are, pronounced like the name of the letter r (Wiktionary)

Examples

  • An uncharged black hole has no inner horizon; it should come as no surprise, then, that as you increase the charge (keeping the mass of the black hole fixed), the two horizons at r+ and r - come together.

    Where Does the Entropy Go?

  • In an extremal black hole, where all of the energy comes from the electric field itself, the two horizons coincide: we have r+ = r - (extremality).

    Where Does the Entropy Go?

  • A representation r is maximally consistent if and only if r is consistent and for any representation r², either r & not-r² is not consistent or r & r² is not consistent (assuming the appropriate conceptions of the negation and conjunction of representations).

    Possible Objects

  • [0, X], and r, r², are real numbers such that r and r² fall in the closed interval

    Bell's Theorem

  • Also take the quantities q, q², r, r² of the above lemma (11) to be the single expectation values:

    Bell's Theorem

  • This rule is conveniently expressed by the formula ((x + 9)/28) _r, in which x denotes the date, and the symbol r denotes that the remainder, which arises from the division of x + 9 by 28, is the number required.

    Encyclopaedia Britannica, 11th Edition, Volume 4, Part 4 "Bulgaria" to "Calgary"

  • He commences slowly, as if repeating the syllable, _de de de de de de d 'd' d 'd' d 'd' d 'r' r 'r'_, -- increasing in rapidity, and at the same time rising as it were by semi-tones, or chromatically, to about a major fourth on the scale.

    The Atlantic Monthly, Volume 2, No. 14, December 1858

  • She ate her dinner quite contentedly, and was just going to settle down comfortably to some thrilling tale of adventure when Br -- r-- r! went the bell, and she knew her fate had descended upon her.

    The Governess

  • _Fa-rewe ` ll lo-ue a ` nd a-ll thi ` e la-wes fo ` r e-ve ` r_

    The Arte of English Poesie

  • The air is full of the rattle of the cicada, which is like the sound of a loud cricket, or the 'r-- r' of a corncraik's note going on for ever and ever; and the house lizard in the church goes cheep -- cheep -- cheep every now and then.

    From Edinburgh to India & Burmah

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