Or search: ossified, fossilized, inflexible
3 Syllables: SUU
authorise, authorize, codified, colonize, dramatize, homicide, modified, modifies, mollified, prophesied, qualified, qualifies
4 Syllables: USUU
apologise, apologize, disqualified, economize, hypothesized, monopolize, personified, unauthorized

Found 20 words across 2 groupings. Skipped 5 excess words of a similar stem.