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

   Synonyms

   • roentgen, R

   Less specific

   • radioactivity unit

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

   Synonyms

   • gas constant, universal gas constant, R

   Less specific

   • constant

3. the 18th letter of the Roman alphabet

   Synonyms

   • R

   Less specific

   • letter, letter of the alphabet, alphabetic character

   Member of

   • Roman alphabet, Latin alphabet

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

   Synonyms

   • radius

   Less specific

   • length

   More specific

   • semidiameter, radius of curvature

   Part of

   • diameter, diam