R

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