R

/ˈɑː/

/ˈɑɹ/

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

synonyms : radius

the 18th letter of the Roman alphabet

synonyms : 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

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

r

/ˈɑː/

/ˈɑːɹ/

describing a motion picture that people under the age of 17 need a guardian or parent in order to watch it

Examples

1. I have a hard time getting my tongue around a lot of Spanish words because I can't roll my R's.

2. r a severe injury

3. R: C'm on.

4. Where r is this thing right there.