| Acronym | Definition |
|---|
| R | Right |
| R | River |
| R | Reverse (automatic transmissions) |
| R | Republican |
| R | Registered Trademark (usually written ®) |
| R | Restricted Audiences - under 17 years of age not permitted without parent/guardian (movie rating) |
| R | Are |
| R | Real (Brazilian currency) |
| R | Red |
| R | Rate |
| R | Required |
| R | Run (baseball/softball) |
| R | Request |
| R | Receive |
| R | Radio |
| R | Range |
| R | Ring |
| R | Rare |
| R | Received (logging abbreviation) |
| R | Racing (car version) |
| R | Risk Assessment |
| R | Radio Operator |
| R | Thursday (using one letter for each day of week) |
| R | Russian (rabbit breed) |
| R | Rural |
| R | Relevant (polygraphy) |
| R | Rear |
| R | Resistance |
| R | Router |
| R | Set of Real Numbers (math) |
| R | Romeo (aviation letter code) |
| R | Restricted |
| R | Radical (chemistry) |
| R | Runner (Mic-O-Say, Heart of America Council, Boy Scouts of America) |
| R | Routine |
| R | Reliability |
| R | Rex (Latin: King) |
| R | Regina (Latin: Queen) |
| R | Rain (weather reports) |
| R | Reset |
| R | Reject |
| R | South African Rand (national currency) |
| R | Routine (logging abbreviation) |
| R | Rabbi |
| R | Radius |
| R | Reuters |
| R | Rookie (sports) |
| R | Reprint |
| R | Manitoba (postal code designation, Canada) |
| R | Respectfully (closing salutation) |
| R | Rua (Portuguese: street; postal usage) |
| R | Reinforcing |
| R | Radial (ply tire) |
| R | Referee |
| R | Resistor |
| R | Rebound (basketball) |
| R | Rook (Chess) |
| R | Search Radius (US DoD) |
| R | Arginine (amino acid) |
| R | Roughness |
| R | Recibo (Portugese) |
| R | Radar Contact (aviation) |
| R | Gas Constant (physical constant) |
| R | Hydrocarbon (functional group) |
| R | Rimmed |
| R | Reception Year (UK schools) |
| R | Rupees |
| R | Repeatability |
| R | Rhizopus (fungi) |
| R | Reflectance |
| R | Roentgen (unit of radiation exposure) |
| R | Aeronca Aircraft Corporation (manufacturer's symbol; US Navy) |
| R | Rankine (Degree) |
| R | Rifampicin |
| R | Respirations |
| R | Rehydratable (food) |
| R | Radiancy |
| R | Research Octane |
| R | Ramp Time (wireless communication) |
| R | Read/er |
| R | Brunswick-Balke-Callender (aircraft company; manufacturer's symbol) |
| R | Resuspension Factor |
| R | Radial Antenna |
| R | Confidential - Restricted Data (TMINS) |
| R | US Revenue Stamp (Scott Catalogue prefix; philately) |
| R | Corrected search radius ('R nought'; R rounded up) |
| R | Route Tuned NAVAID (aviation) |
| R | Réaumier (temperature scale named after the French scientist Rene Antoine Ferchault de Reaumur) |
| R | US DoT tire speed rating (106 mph) |
| R | Third Heartbeat Wave |