R

noun

1. 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.quantity

   Synonyms roentgen

   Source: WordNet 3.0

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

   noun.quantity

   Synonyms gas constant universal gas constant

   Source: WordNet 3.0

3. the 18th letter of the Roman alphabet

   noun.communication

   Source: WordNet 3.0

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

   noun.attribute

   Synonyms radius

   Source: WordNet 3.0