#1 r n. [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. wn
#2 r 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. wn
#3 r n. [R] the 18th letter of the Roman alphabet. wn
#4 r n. [R] the 18th letter of the Roman alphabet. wn
#5 r n. [radius] the length of a line segment between the center and circumference of a circle or sphere. wn
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