R

1.

R, the eighteenth letter of the English alphabet, is a vocal consonant. It is sometimes called a semivowel, and a liquid. See Guide to Pronunciation, 178, 179, and 250-254. The three Rs a jocose expression for reading, (w)riting, and (a)rithmetic, - the fundamentals of an education.

Noun	1.	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 Synonyms: roentgen
	2.	R - (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
	3.	R - the 18th letter of the Roman alphabet
	4.	r - the length of a line segment between the center and circumference of a circle or sphere Synonyms: radius

radioactivity unit, roentgen