R
Pronunciation: är
| 1. | 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.
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| Noun | 1. | R - a unit of radiation exposure; the dose of ionizing radiation that will produce 1 electrostatic unit of electricity in 1 cc of dry air Synonyms: roentgen |
| 2. | R - (physics) the universal constant in the gas equation: pressure times volume = R times temperature; equal to 8.3143 joules per kelvin per mole Synonyms: gas constant, universal gas constant | |
| 3. | R - the 18th letter of the Roman alphabet | |
| 4. |  r - the length of a line segment between the center and circumference of a circle or sphereSynonyms: radius |