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R (iou)



R, r. [¨»:]
The eighteenth letter of the modern English alphabet and the seventeenth of the ancient Roman one, is derived through early Greek ¦Ñ from Phoenician, repr. the twentieth letter of the early Semitic alphabet. In general R denotes a post-alveolar voiced consonant, in the formation of which the point of the tongue approaches the palate a little way behind the teeth; in many languages this is accompanied by a vibration of the tongue, in which case the R is said to be 'trilled' or 'rolled'. This trill is almost or altogether absent in the R of mod. standard British English, which moreover retains its consonantal value only when it precedes a vowel (see linking r s.v. LINKING 1); in other positions it has been vocalized to an sound, and even this is entirely lost after certain vowels. In Scotland R is still often strongly trilled in all positions, and other varieties of the sound are characteristic of certain districts of the UK. In other parts of the English-speaking world there are similarly varieties both with R only before vowels and with retention of its consonantal value in other historical positions. By southern British speakers R is frequently introduced between word-final and word-initial vowels (see intrusive r s.v. INTRUSIVE adjective 2). In all periods of English, R has exercised a marked effect on a preceding vowel, in modern English being associated with the lengthening of it. Pl. R's, Rs.
I.
The letter and its sound.
r-colour the modification of a vowel sound caused by a following r, with retraction of the tongue, as in one US pronunciation of bird. r month a month in whose name an r appears, as being one of those (September to April) during which oysters are in season. the three R's reading, writing, and arithmetic (as the basis of elementary education).
II. Symbolical uses.
Used to denote serial order; applied e.g. to the eighteenth (or often the seventeenth, either I or J being omitted) group or section, sheet of a book, etc.
Chemistry. [Abbreviation of radical.] (Cap. R.) In chemical formulae, an unspecified radical or group of radicals (usu. organic).
Physical Chemistry. (Cap. R.) The gas constant.
Biology. (Italic r.) The rate of increase of a population, usually representing the factor by which its size is multiplied in each generation, or the value which this factor would have if resources were unlimited.
r selection the form of natural selection which acts on populations having ample resources and little or no competition.
Physics. (Cap. R.) The Rydberg constant.
Chemistry. [Abbreviation of Latin rectus right.] (Cap. R.) Designating (compounds having) a configuration about an asymmetric carbon atom in which the substituents, placed in order according to certain rules, form a clockwise sequence when viewed from a particular direction. Opp. S, S 10.
Astronomy. [Initial letter of rapid.] r-process, a process believed to occur in stars in circumstances of high neutron flux (e.g. in supernova explosions), in which heavy atomic nuclei are formed from lighter ones by a combination of rapid neutron captures and slower beta decays. Opp. s-process.
Microbiology. [Initial letter of resistance.] (Cap. R.) Denoting certain plasmids which confer drug-resistance on bacteria and can be transferred to other bacteria by conjugation.
III.
Abbrevs.: R = Rabbi; radius; Railway; rand(s) (as monetary unit); Reaumur; (Medicine) Recipe; Regiment; Regina; registered (of a trade mark); (US) Republican; restricted (in US film classification); reverse (on the selector mechanism in a motor vehicle); Rex; right (as opp. left); River; roentgen; (Chess) rook; Royal (in names of organizations). = (Medicine) Recipe; (Ecclesiastical) Response. = registered (of a trade mark). r = radius (vector); (Nautical) rain (in a logbook); recto; right (as opp. left); run(s) (in cricket).