R Very Common

a unit of radiation exposure; the dose of ionizing radiation that will produce 1 electrostatic unit of electricity in 1 cc of dry air

(physics) the universal constant in the gas equation: pressure times volume = R times temperature; equal to 8.3143 joules per kelvin per mole

the 18th letter of the Roman alphabet

the length of a line segment between the center and circumference of a circle or sphere

radius

are (in text messaging and internet conversations)

restricted

The eighteenth letter of the English alphabet, called ar and written in the Latin script.

The ordinal number eighteenth, derived from this letter of the English alphabet, called ar and written in the Latin script.