2 Syllables: SU
bismuth, bridges, busiest, business, Christmas, dishes, fishes, fitness, Griffith, isthmus, kisses, listless, mischief, mistress, piteous, prettiest, quickness, riches, richest, richness, ridges, sickness, stiffness, strictest, strictness, swiftest, swiftness, switches, thickness, vicious, visage, viscous, vistas, witches, witness
3 Syllables: USU
ambitious, auspicious, capricious, delicious, eyewitness, factitious, fictitious, forgiveness, initiates, judicious, lascivious, malicious, Mauritius, Narcissus, nutritious, oblivious, officious, pernicious, prestigious, prodigious, propitious, religious, seditious, suspicious, unfitness
4 Syllables: UUSU
adventitious, avaricious, Dionysius, expeditious, injudicious, irreligious, superstitious, surreptitious, unpropitious, unsuspicious
Found 70 words across 3 groupings. Skipped 2 excess words of a similar stem.