2 Syllables: SU
Ceres, cheery, clearly, dearly, decrease, dreary, eerie, Erie, fiercely, fieri, iri, merely, nearly, Petri, queried, queries, query, series, Siegfried, theories, theory, wearied, weary, wiry, yearly
3 Syllables: SUU
cheerily, fearfully, seriously
3 Syllables: USU
machinery, severely, sincerely, unwearied
4 Syllables: USUU
imperiously, materially, mysteriously

Found 35 words across 4 groupings. Skipped 1 excess word of a similar stem.