Nouns

(n)roentgen, Ra unit of radiation exposure; the dose of ionizing radiation that will produce 1 electrostatic unit of electricity in 1 cc of dry air
(n)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
(n)R, rthe 18th letter of the Roman alphabet