Or search: rex
2 Syllables: SU
7, aaron, airing, baring, baron, barren, bearing, beckon, bedding, bedlam, begging, bellum, betting, blessing, bremen, brethren, breton, caring, cession, charing, checking, clarence, clemens, clement, crescent, currant, daring, deaden, deadening, deference, denning, destined, devon, dreading, dredging, dressing, dwelling, ebbing, edging, edmond, edmund, ellen, epsom, errand, errant, erring, essen, essence, etching, evan, extant, felling, felon, fetching, flaring, fleming, freshened, fretting, getting, glaring, guessing, harem, heading, heaven, helen, helen's, heron, herring, hessian, jennings, jesting, karen, larynx, leaden, leaven, leben, legend, lemon, lenin, lessen, lessing, lesson, letting, leveling, levin, meddling, melon, nesting, nestling, netting, pairing, parent, paring, peasant, pecking, pelham, penance, pennant, pharynx, pheasant, pleasant, pledging, plenum, preference, pregnant, presence, present, pressing, pression, preston, question, reading, reckon, reckoning, reckons, rectum, reddened, reference, requiem, resin, resting, reverend, second, section, segment, selling, septum, session, setting, settling, seven, sexton, sharing, sharon, shedding, shelling, sketching, smelling, sparing, spectrum, spelling, spreading, squaring, staring, stemming, stephens, stepping, stressing, stretching, swearing, sweating, swelling, tearing, telling, tenant, terence, testing, threading, threaten, threatening, threatens, threshing, treading, vellum, venom, vesting, veteran, vexing, weapon, wearing, wedding, welling, weren, weston, wetting, wrecking, wresting, wrestling, yelling
3 Syllables: SUU
3 Syllables: USU
aberrant, abetting, acceptance, accepting, accession, addressing, affecting, affection, aggression, alleging, annexing, apparent, arresting, assessing, assessment, attesting, begetting, besetting, caressing, clandestine, collecting, collection, comparing, compelling, complexion, compressing, compression, conception, concession, condemning, confessing, confession, connecting, connection, connexion, consenting, contestants, contesting, convection, correcting, correction, deception, declaring, defection, deflection, dejection, depressing, depression, descendants, despairing, detecting, detection, digression, discretion, dispelling, dissecting, dissenting, distressing, ejection, electing, election, endeavoring, erecting, erection, excelling, excepting, exception, expectant, expecting, expelling, expressing, expression, fluorescent, forbearance, forbearing, foretelling, forgetting, impairing, impelling, impressing, impression, inception, incessant, indwelling, infecting, infection, inflection, inherent, injecting, injection, inspecting, inspection, intestine, investing, investment, lieutenant, magellan, neglecting, objecting, objection, obsession, oppressing, oppression, perception, perfecting, perfection, perplexing, possessing, possession, predestined, preparing, preventing, procession, professing, profession, progressing, progression, projecting, projection, propelling, prospecting, protecting, protection, quiescence, quiescent, quintessence, rebelling, reception, recession, reflecting, reflection, reflexion, refreshing, regression, regretting, rejecting, rejection, repairing, repellent, repelling, repressing, repression, requesting, resenting, respecting, secession, selecting, selection, subjecting, subjection, succession, suggesting, suppressing, suppression, suspecting, transgressing, transgression, transparent, undressing, unerring, unpleasant, unsettling, unsparing, upsetting
4 Syllables: UUSU

Found 391 words across 4 groupings. Skipped 91 excess words of a similar stem.