2 Syllables: SU
biggest, bigness, citrus, fitness, fittest, hideous, idioms, igneous, Indians, India's, mixes, Nicholas, nitrous, piteous, prettiest, quibus, quickness, sickness, strictest, strictness, thickness, vitreous, witness
3 Syllables: USU
amphibious, assiduous, eyewitness, fastidious, insidious, invidious, Mauritius, perfidious, unfitness
Found 32 words across 2 groupings. Skipped 2 excess words of a similar stem.