2 Syllables: SU
biggest, bigness, bigots, billets, biscuits, bishops, Christmas, citrus, dearest, digits, fitness, fittest, frigates, grimace, hideous, hillocks, igneous, isthmus, limits, listless, minutes, minutest, mistress, mixes, nearest, Nicholas, nitrous, Philips, pickets, piteous, prettiest, quibus, quickness, richest, rivets, sickness, spinach, strictest, strictness, thickets, thickness, tickets, vicious, viscous, vitreous, witness
3 Syllables: USU
ambitious, amphibious, archbishops, assiduous, auspicious, bacillus, capricious, delicious, elicits, enigmas, exhibits, eyewitness, factitious, fastidious, fictitious, inhibits, insidious, invidious, judicious, malicious, Mauritius, Narcissus, nutritious, officious, perfidious, pernicious, prestigious, prodigious, prohibits, propitious, religious, seditious, severest, sincerest, suspicious, unfitness, utilise
4 Syllables: UUSU
adventitious, avaricious, expeditious, injudicious, irreligious, superstitious, surreptitious, unpropitious, unsuspicious
Found 92 words across 3 groupings. Skipped 4 excess words of a similar stem.