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2 Syllables: SU
clearance, deviant, Ephraim, fearsome, ference, Pearson, serum, theorem
3 Syllables: USU
achievement, adherence, adherent, appearance, bereavement, coherence, coherent, imperium, Macpherson, magnesium, reappearance
4 Syllables: UUSU
disappearance, incoherence, incoherent, interference, perseverance

Found 24 words across 3 groupings. Skipped 3 excess words of a similar stem.