r

Noun

• the length of a line segment between the center and circumference of a circle or sphere

• the 18th letter of the Roman alphabet

• (physics) the universal constant in the gas equation: pressure times volume = R times temperature; equal to 8.3143 joules per kelvin per mole

• a unit of radiation exposure; the dose of ionizing radiation that will produce 1 electrostatic unit of electricity in 1 cc of dry air

Related words

• Synonyms: 
  radius , R , gas constant , universal gas constant , roentgen