Define:

R (http://definr.com/R)

n 1: a unit of radiation exposure; the dose of ionizing radiation

that will produce 1 electrostatic unit of electricity in

1 cc of dry air [syn: roentgen, R]

2: (physics) the universal constant in the gas equation:

pressure times volume = R times temperature; equal to

8.3143 joules per kelvin per mole [syn: gas constant, {universal

gas constant}, R]

3: the 18th letter of the Roman alphabet [syn: R]

4: the length of a line segment between the center and

circumference of a circle or sphere [syn: radius]