Or search: timid, trepid, fearful
2 Syllables: SU
interests, Nicholas
3 Syllables: SUU
bitterest, frivolous, limitless, rigorous, Spiritus, syllabus, vigorous, villainous
4 Syllables: USUU
antithesis, carnivorous, felicitous, indigenous, solicitous, vociferous
5 Syllables: UUSUU
abolitionist

Found 17 words across 4 groupings. Skipped 1 excess word of a similar stem.