2 Syllables: SU
Nicholas
3 Syllables: SUU
bitterest, frivolous, limitless, rigorous, Spiritus, syllabus, timorous, vigorous, villainous, vividness
4 Syllables: USUU
antithesis, carnivorous, Elizabeth, Elizabeth's, felicitous, indigenous, solicitous, vociferous
5 Syllables: UUSUU
abolitionist

Found 20 words across 4 groupings. Skipped 1 excess word of a similar stem.