|r or R (ɑː)|
|—n , pl r's, R's, Rs|
|1.||the 18th letter and 14th consonant of the modern English alphabet|
|2.||a speech sound represented by this letter, in English usually an alveolar semivowel, as in red|
|3.||See three Rs|
|R or R|
|3.||Réaumur temperature (scale)|
|4.||physics, electronics resistance|
|5.||roentgen or röntgen|
|8.||chem gas constant|
|9.||in the US and Australia|
|a. restricted exhibition (used to describe a category of film certified as unsuitable for viewing by anyone under the age of 18)|
|b. (as modifier): an R film|
|3.||Also: r rod (unit of length)|
|5.||cricket, baseball run(s)|
|5.||response (in Christian liturgy)|
|[(sense 6) Latin: King]|
|R. or r.|
|r. or r.|
radical (usually an alkyl or aryl group)
respiratory exchange ratio
or r roentgen
Abbreviation of radius
The symbol for resistance.
see three R's.
unit of X-radiation or gamma radiation, the amount that will produce, under normal conditions of pressure, temperature, and humidity, in 1 kg (2.2 lbs) of air, an amount of positive or negative ionization equal to 2.58104 coulomb. It is named for the German physicist Wilhelm Conrad Rontgen. See also rem.
Learn more about R with a free trial on Britannica.com.