Or search: tough, knotty, elusive, baffling, debatable, problematic, questionable
3 Syllables: SUU
capital, Capitol, classical, graphical, Hannibal, magical, practical, radical, tactical, tragical
4 Syllables: USUU
botanical, dynamical, fanatical, fantastical, grammatical, impractical, irascible, mechanical, theatrical, tyrannical
5 Syllables: UUSUU
biographical, enigmatical, geographical, mathematical, piratical, puritanical, topographical, typographical
6 Syllables: UUUSUU
ecclesiastical
7 Syllables: UUUUSUU
autobiographical

Found 30 words across 5 groupings. Skipped 3 excess words of a similar stem.