• noun:   the 18th letter of the Roman alphabet
• noun:   the length of a line segment between the center and circumference of a circle or sphere
• noun:   a unit of radiation exposure; the dose of ionizing radiation that will produce 1 electrostatic unit of electricity in 1 cc of dry air
• noun:   (physics) the universal constant in the gas equation: pressure times volume = R times temperature; equal to 8.3143 joules per kelvin per mole

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