rachitic, rachiotomy, rachiopathy, rachiometer, rachiochysis

radiate, radioactive, radio, radiography, radioisotope, radiometric, radioscopy, radiotherapy

redolent, redintegrate, render, receive, recommend, recover, recreate, refer, remain, request, require, recovery

retroactive, retrofit, retroflex, retrograde, retro-rocket, retrospect, retrospection, retroversion, retrovirus

rheology, rheostat, rheometer