| 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 | |
| 2. | R - (physics) the universal constant in the gas equation: pressure times volume = R times temperature; equal to 8.3143 joules per kelvin per moleconstant - a number representing a quantity assumed to have a fixed value in a specified mathematical context; "the velocity of light is a constant" | |
| 3. | R - the 18th letter of the Roman alphabetLatin alphabet, Roman alphabet - the alphabet evolved by the ancient Romans which serves for writing most of the languages of western Europe | |
| 4. | r - the length of a line segment between the center and circumference of a circle or spherediam, diameter - the length of a straight line passing through the center of a circle and connecting two points on the circumference semidiameter - the apparent radius of a celestial body when viewed as a disc from the earth radius of curvature - the radius of the circle of curvature; the absolute value of the reciprocal of the curvature of a curve at a given point length - the linear extent in space from one end to the other; the longest horizontal dimension of something that is fixed in place; "the length of the table was 5 feet" | |