| R | Reinforcing - Right -R?ntgen | - | Astronomy |
| R&B | Rhythm And Blues | - | Astronomy |
| R&D | Research & Development | - | Astronomy |
| R&R | Rest & Relaxation | - | Astronomy |
| R&S | Reconnaissance & Surveillance | - | Astronomy |
| R2I | Resistance To Interrogation | - | Astronomy |
| R3P | Rearm | - | Astronomy |
| RA | Radium | - | Astronomy |
| RA | Rain (METAR Code) -Rear Area - Reinforced Alert - Republican Army - Right Ascension - Royal Artillery (UK) - Royal Academy | - | Astronomy |
| RAA | Rear Assembly Area | - | Astronomy |
| RAAF | Royal Australian Air Force | - | Astronomy |
| RAC | Royal Automobile Club (in The United Kingdom | - | Astronomy |
| RACK | Risk Aware Consensual Kink (SM Phrase) | - | Astronomy |
| RACON | RAdar BeaCON | - | Astronomy |
| RADAR | RAdio Detection And Ranging | - | Astronomy |
| RADB | Real America Database - Resource Assessment Database - Reunion Address DataBase - Rice Allelopathy Data Base - Routing Arbiter Data Base | - | Astronomy |
| RADB | Routing Assets Data Base | - | Astronomy |
| RADB | Rad51/Dmc1 Homologous Protein | - | Astronomy |
| RADC | Region Air Defence Commander | - | Astronomy |
| RAE | UK Royal Aircraft Establishment (?1991) | - | Astronomy |
| RAF | Red Army Faction - Royal Air Force | - | Astronomy |
| RAG | Raising And Giving - Rocket Antitank Grenade | - | Astronomy |
| RAM | Random Access Memory - Rolling Airframe Missile - Royal Air Maroc | - | Astronomy |
| RAMARK | RAdar MARKer | - | Astronomy |
| RAOC | Rear Area Operation Centre | - | Astronomy |
| RAP | Radio Access Point - Radiological Assistance Program (U.S. Department Of Energy) - Rear Area Protection - Recognised [Operating/Operational] Air Picture - Recurring Advance Payment - Relational Associative Processor - Reliable Acoustic Path - Rocket-Assis | - | Astronomy |
| RARDE | UK Royal Armament Research And Development Establishment (1962?1991) | - | Astronomy |
| RATELO | Radiotelephone Operator | - | Astronomy |
| RB | Running Back (football) | - | Astronomy |
| RB | Rubidium | - | Astronomy |
| RBCI | Radio Based Combat Identification | - | Astronomy |
| RBI | Runs Batted In | - | Astronomy |
| RBOC | Regional Bell Operating Company (Baby Bell) | - | Astronomy |
| RC | See Entry | - | Astronomy |
| RCA | Radio Corporation Of America - Root Cause Analysis - Royal Canadian Artillery - Royal City Avenue (famous Entertainment Zone In Thailand) | - | Astronomy |
| RCAF | Royal Canadian Air Force | - | Astronomy |
| RCAR | Research Council For Automobile Repairs (are-car) | - | Astronomy |
| RCC | Rescue Co-ordination Centre | - | Astronomy |
| RCCO | Royal Canadian College Of Organists | - | Astronomy |
| RCHA | Royal Canadian Horse Artillery (regiment) | - | Astronomy |
| RCMP | Royal Canadian Mounted Police | - | Astronomy |
| RCRA | Resource Conservation And Recovery Act (reck-ra Or Rick-ra) | - | Astronomy |
| RCS | Radar Cross-Section - Revision Control System - Reaction Control System | - | Astronomy |
| RCT | Randomized Controlled Trial - Robotically Controlled Telescope | - | Astronomy |
| RCZ | Rear Combat Zone | - | Astronomy |
| RD | Radio Disney | - | Astronomy |
| RDA | Research | - | Astronomy |
| RDD | Radiological Dispersion Device | - | Astronomy |
| RDDL | Resource Directory Description Language (riddle) | - | Astronomy |
| RDECOM | (U.S.) Research | - | Astronomy |
| RDM | Remotely Delivered/Deliverable Mine | - | Astronomy |
| RDO | Rapid | - | Astronomy |
| RDT | Remote Digital Terminal | - | Astronomy |
| RDTE OR RDT&E | Research | - | Astronomy |
| RDV | Remote Detection Vehicle | - | Astronomy |
| RE | Rhenium | - | Astronomy |
| RE | Royal Engineers | - | Astronomy |
| REACH | Registration | - | Astronomy |
| REACT | Remote Electronically Activated Control Technology | - | Astronomy |
| REAM | Retired Educators Association Of Minnesota | - | Astronomy |
| REEF | Reef Environmental Education Foundation | - | Astronomy |
| REM | Rapid Eye Movement (sleep Phase) - Rosicrucian Egyptian Museum | - | Astronomy |
| REME | Royal Electrical And Mechanical Engineers | - | Astronomy |
| RERC | Rehabilitation Engineering Research Center | - | Astronomy |
| RES | Radiation Exposure Status -Reserve | - | Astronomy |
| RESNA | Rehabilitation Engineering And Assistive Technology Society Of North America | - | Astronomy |
| REU | R?union (ISO 3166 Trigram) | - | Astronomy |
| RF | Radio Frequency - Receptive Field (neurophysiology) | - | Astronomy |
| RF | Rutherfordium | - | Astronomy |
| RFA | Restrictive Fire Area (military) - Royal Field Artillery | - | Astronomy |
| RFC | Request For Comments - Royal Flying Corps (WWI Precursor To RAF) | - | Astronomy |
| RFE | Request For Enhancement | - | Astronomy |
| RFEF | Real Federaci›n Espa?ola De Fœtbol (Spanish For Royal Spanish Football Federation) | - | Astronomy |
| RFI | Ready For Inspection - Ready For Issue - Request For Information - Radio Frequency Interference | - | Astronomy |
| RFID | Radio Frequency IDentification | - | Astronomy |
| RFL | Restrictive Fire Line (military) | - | Astronomy |
| RG | Republican Guard | - | Astronomy |
| RG | Roentgenium | - | Astronomy |
| RGB | Red Green Blue (colour Model) | - | Astronomy |
| RGBI | Red Green Blue Intensity (ditto) | - | Astronomy |
| RH | Rhodium | - | Astronomy |
| RH | Southern Rhodesia (ISO 3166 Digram; Obsolete 1980) | - | Astronomy |
| RHIC | Relativistic Heavy Ion Collider | - | Astronomy |
| RHLI | Royal Hamilton Light Infantry (Canadian Militia Regiment) | - | Astronomy |
| RHO | Southern Rhodesia (ISO 3166 Trigram; Obsolete 1980) | - | Astronomy |
| RHS | Right Hand Side - Redland High School | - | Astronomy |
| RHU | Replacement Holding Unit | - | Astronomy |
| RHWR | Radar Homing And Warning Receiver (raw For Short) | - | Astronomy |
| RI | Rhode Island (postal Symbol) | - | Astronomy |
| RIAA | Recording Industry Association Of America | - | Astronomy |
| RIF | Reduction In Force (layoffs) - Resistance Index For Frostbite | - | Astronomy |
| RIMVS | Retinal Imaging Machine Vision System | - | Astronomy |
| RIP | Relief In Place -requiesca[n]t In Pace (Latin For May He/she/they Rest In Peace) | - | Astronomy |
| RIS | Range Instrumentation System | - | Astronomy |
| RISC | Reduced Instruction Set Computer | - | Astronomy |
| RISD | Rhode Island School Of Design (riz-dee) | - | Astronomy |
| RISTA | Reconnaissance | - | Astronomy |
| RJD | Reduced Julian Day | - | Astronomy |
| RKBA | Right To Keep And Bear Arms (Second Amendment To The United States Constitution) | - | Astronomy |
| RKO | Radio-Keith-Orpheum Pictures | - | Astronomy |
