@freemo @peterdrake

R you sure?

Science
Biology and medicine
Arginine, an amino acid
ATC code R Respiratory system, a section of the Anatomical Therapeutic Chemical Classification System
Coefficient of relationship (r), in biology
Effective reproduction number (R), the number of cases generated by one case in the current state of a population in epidemiology
Basic reproduction number (R0), the expected number of cases directly generated by one case
Haplogroup R (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup
Haplogroup R (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup
Net reproduction rate (R0), the average number of offspring that would be born to a female given conforming conditions
r, the population growth rate in the r/K selection theory of ecology
Astronomy
Spectral resolution ({\displaystyle \mathbb {R} }\mathbb {R} ), in astronomy
Orangish or K carbon stars (stellar classification: R)
Physics
R (cross section ratio), the ratio of hadronic to muonic cross sections
Electrical resistance (R)
Roentgen (unit) (R), a unit of measurement for ionizing radiation such as X-ray and gamma rays
Rydberg constant (R∞, RH), a physical constant relating to energy levels of electrons within atoms
Rydberg unit of energy (Ry), the energy of the photon whose wavenumber is the Rydberg constant
Temperature scales
Rankine scale (°R, °Ra)
Réaumur scale (°Ré, °Re, °r)
Rømer scale (°R, °Rø)
Chemistry
Gas constant (R), in chemistry
R, one of two chiral center configurations in the R/S system
Side chain (an unspecified group of atoms), in a chemical or structural formula
Mathematics
r is the symbol for the radius of a circle
{\displaystyle \mathbb {R} }\mathbb {R} or R, the set of all real numbers
Pearson product-moment correlation coefficient (r), in statistics
Ricci curvature
Technology and engineering
R-value (insulation), a non-SI measure of thermal resistance used in housing insulation
R-value (soils), property of soils used in pavement design
Resistor, an electronic component
R-, a refrigerant numbering system
R, the ratio between the minimum and maximum stresses in fracture mechanics
R- or recall-button, now mostly used to switch between two calls
Computing
R (programming language), an environment for statistical computing and graphics
R (complexity), the set of all recursive languages
IBM System R, an IBM database system
RequestBot, a service in QuakeNet's IRC services
Arts and entertainment
Music
Ritardando, a term for slowing the tempo down gradually
R. (R. Kelly album), a 1998 album by R. Kelly
R° (Ruratia album), a 2002 album by Rurutia
R (single album), a 2021 single album by Rosé
Rated R (Queens of the Stone Age album), 2000 album also called R
R (jp), 2005 J-Pop album by Ryoko Shiraishi
Film
R (film), a 2010 film by Danish screenwriter and film director Tobias Lindholm
R, a character played by John Cleese in The World Is Not Enough
R, the protagonist of Warm Bodies, based on the book of the same name
R, a film rating in the Motion Picture Association of America film rating system and in the Canadian Home Video Rating System
Television
Rajawali Televisi (RTV), television in Indonesia
R, the production code for the 1965 Doctor Who serial The Chase
Video games
R·Type, an arcade video game
R: Rock'n Riders, in the list of PlayStation games (M–Z)
Organisations
The Crown, Rex (King) or Regina (Queen) in Commonwealth nations
Ryder (NYSE ticker symbol)
R (cable operator), a telecommunications company
R, denoting a member of the US Republican Party
Transportation
Nissan Skyline GT-R, commonly referred to as the R in Japan
R (New York City Subway service)
Reconnaissance aircraft (military designation: R)
Restricted airspace
Volkswagen R, the performance division of Volkswagen
Other uses
Registered trademark symbol (®)
South African rand (R), a currency
Right (direction)
Rolled R (IPA: r), the alveolar trill of Spanish, Italian, & Arabic languages
UTC−05:00 (military time zone code: Romeo)
Я, a Cyrillic letter similar to R

(source: wikipedia)