Or search: ism, credo, creed, dogma, gospel, monism, animism, dualism, precept, dynamism, feminism, humanism, nihilism, pacifism, populism
2 Syllables: SU
Auckland, auction, audience, autumn, bottom, boxes, Brabant, broaden, Cochrane, cotton, Dobson, doctrine, Falkland, foxes, Fox's, gotten, Hobson, Houghton, Ogden, option, oxen, problem, quadrant, Robin, rotten, Scotchman, Scotland, Scotsman, shotgun, sodden, Sodom, squadron, Stockton, trodden, Watson, Watson's
3 Syllables: USU
adoption, allotment, concoction, downtrodden, forgotten, untrodden

Found 42 words across 2 groupings. Skipped 10 excess words of a similar stem.