- 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
--1 is a kind of radioactivity unit
- 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
--2 is a kind of constant
- R - the 18th letter of the Roman alphabet
--3 is a kind of letter, letter of the alphabet, alphabetic character
--3 is a member of Roman alphabet, Latin alphabet- radius, r - the length of a line segment between the center and circumference of a circle or sphere
--4 is a kind of length
--4 is a part of diameter, diam
--4 has particulars: semidiameter; radius of curvature - radius, r - the length of a line segment between the center and circumference of a circle or sphere