| radius | beam, spoke |  | radi- | radius, radiāre | radiance, radiation |
| rancere | rancidness, grudge, bitterness |  | ranc- | rancere | rancid, rancor |
| rapere | rob, seize |  | rap- | rapere, raptus | arreption, arreptitious, enrapt, enrapture, rapacious, rapacity, rape, rapid, rapidity, rapine, rapt, raptio, raptor, raptorial, rapture, rapturous, raptus, ravenous, ravine, ravish, subreption, subreptitious, surreptitious |
| raucus | harsh, hoarse |  | rauc- | raucus | raucous |
| re- | again, back |  | re-, red- | re- | recede, redact |
| regere | straight, direct |  | rect-, reg-, -rig- | regere “to direct, lead straight, guide”, related rectus “straight, right” | correct, direct, dirigible, erect, erection, ergo, rectangle, rectify, rectitude, rectum, regent, regime, regimen, regiment, region, surge |
| residere | left behind |  | resid- | residere “remain behind” (see also sedere) | reside, residence, resident, residual, residue |
| retrō | backward, behind |  | retro- | retrō | retrograde, retrospective, retrovirus |
| rex | king |  | reg-, rex- | rex (genitive regis) | regal, regency, regicide, Regis, regulation, reign, rex, royal |
| ridere | laugh |  | rid-, ris- | ridere “to laugh” (past participle risus) | deride, derision, ridicule, ridiculous, risible |
| rogāre | ask |  | rog- | rogāre | abrogate, arrogant, arrogate, derogate, derogation, derogatory, interrogation, prerogative, prorogue, rogation, rogue, surrogate |
| rota | wheel |  | rot- | rota, rotāre | arrondissement, circumrotation, contrarotation, control, controller, decontrol, enroll, enrollee, enrollment, irrotational, multirole, multiroll, redondilla, reenroll, rodeo, role, roll, rondeau, rondel, rondelle, rondo, rotary, rotate, rotation, rotational, rotator, rotatory, rotavirus, rotelle, rotifer, Rotifera, rotiferous, rotiform, rotula, rotund, rotunda, rotundifolious, rotundity, roulette, round, roundel, roundelay, roundlet, rowel, semiround |
| ruber | red |  | ruber-, rubr- | ruber | erubescence, erubescent, rubella, Rubio, rubious, rubric, rubricate, rubrication, rubricator, ruby |
| rudis | unskilled, rough, unlearned |  | rudi- | rudis | erudite, erudition, rude, rudiment, rudimentary, rudity |
| rumpere | break, burst |  | rump-, rupt- | rumpere, ruptus | abrupt, abruption, corrupt, corruptible, corruption, corruptor, disrupt, disruption, disruptive, disruptor, disrupture, erumpent, erupt, eruption, eruptive, incorrupt, incorruptibility, incorruptible, interrupt, interruptible, interruption, irrupt, irruption, irruptive, maleruption, noneruptive, reroute, rout, route, routine, rupture, subroutine, supereruption |
| rāder | scrape, shave |  | rad-, ras- | rādere, rāsus | abrade, abrasion, abrasive, corrade, corrasion, erase, erasure, nonabrasive, radula, radular, raduliform, rase, rash, rasorial, raster, rasure, subradular |
| rādix | root |  | radic- | rādix, rādīcis | eradicate, radical, radix |
| rāmus | branch |  | ram- | rāmus | ramification, rammel, ramose, ramous, ramulose, ramulous |
| rāna | frog |  | ran- | rāna | Rana |
| rāpum | turnip |  | rap- | rāpum | rapeseed |
| rārus | rare |  | rar- | rārus | rarity |
| rēgula | rule |  | regul- | rēgula “to rule” | regular, regulate, regulation, rule |
| rēmus | oar |  | rem- | rēmus | bireme, trireme |
| rēnēs | kidney |  | ren- | rēnēs | renal |
| rēpere | crawl, creep |  | rep-, rept- | rēpere, reptus | reptile |
| rēte | net |  | ret- | rēte | reticle, retina |
| rōborāre | oak, strength |  | robor- | rōborāre “to strengthen”, from rōbur, rōbus “strength” | corroborant, corroborate, corroboration, corroborative, corroborator, robust |
| rōdere | gnaw |  | rod-, ros- | rōdere, rōsus | corrode, erosion, rodent |
| rōstrum | beak, prow |  | rostr- | rōstrum | brevirostrate, curvirostral, lamellirostral, rostellate, rostelliform, rostellum, rostral, rostrate, rostriform, rostrulum, rostrum |
| rūga | wrinkle |  | rug- | rūga, rugare | corrugant, corrugate, corrugation, erugate, rugose |
| rūmen | throat |  | rumin- | rūmen, rūminis | rumen, rumenic acid, ruminal, ruminant, ruminate, rumination, ruminator |
| rūs | countryside, farm |  | rur- | rūs, rūris | nonrural, roister, roisterous, rural, rustic, rusticate, rustication, rusticity |
