Or search: cooperative
2 Syllables: SU
average, fastenings, happenings
3 Syllables: SUU
gatherings, labyrinth, mattresses, narrative, Nazareth, palaces, pasturage, patronage, vassalage
4 Syllables: USUU
commemorative, comparative, deliberative
5 Syllables: USUUU
cooperative

Found 16 words across 4 groupings. Skipped 2 excess words of a similar stem.