r Meaning, Definition & Usage

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

WordNet