2 Syllables: SU
Nicholas
3 Syllables: SUU
bitterest, fickleness, frivolous, limitless, littleness, Michaelmas, rigorous, Spiritus, syllabus, timorous, vigorous, villainous
4 Syllables: USUU
antithesis, carnivorous, felicitous, indigenous, meticulous, ridiculous, solicitous, vociferous
5 Syllables: UUSUU
abolitionist

Found 22 words across 4 groupings. Skipped 1 excess word of a similar stem.