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r
Nounr has 4 senses
roentgen, 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 --1is a kind ofradioactivity unit
gas constant, universal gas constant, R - (physics) the universal constant in the gas equation: pressure times volume = R times temperature; equal to 8.3143 joules per kelvin per mole --2is a kind ofconstant