Definition of R

Noun

• the length of a line segment between the center and circumference of a circle or sphere
  radius
• 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
  - gas constant - universal gas constant
• 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

Word games points for the R

• Scrabble® score of the r (1)
• Word Chums® score of the r (1)
• Words With Friends® score of the r (1)