2 Syllables: SU
biggest, bigness, citrus, dimness, fitness, fittest, hideous, idiots, igneous, Indus, influx, ingots, interests, mixes, Nicholas, nitrous, piteous, prettiest, quibus, quickness, ringlets, sickness, simplest, sinless, sinuous, strictest, strictness, thickness, trinkets, vitreous, witness
3 Syllables: SUU
3 Syllables: USU
amphibious, assiduous, distinctness, enigmas, eyewitness, fastidious, insidious, invidious, Mauritius, Olympus, perfidious, unfitness
4 Syllables: UUSU
Found 46 words across 4 groupings. Skipped 1 excess word of a similar stem.