Or search: file, mail, slate, enrol, enroll, patent, timber, timbre, furnace, recruit, storage, campaign, inscribe, perceive, registry
3 Syllables: SUU
barrister, creditor, editor, registered, registers, severer
4 Syllables: USUU
competitor, progenitor
5 Syllables: UUSUU
primogeniture

Found 9 words across 3 groupings. Skipped 6 excess words of a similar stem.