Or search: urging, insistence, insistency
4 Syllables: SUUU
aphorism, Calvinism, cataclysm, catechism, communism, heathenism, humanism, mannerisms, mechanism, naturalism, organism, paganism, unionism
5 Syllables: USUUU
anachronism, antagonism, determinism, fanaticism, metabolism, sectarianism
7 Syllables: UUUSUUU
utilitarianism

Found 20 words across 3 groupings. Skipped 2 excess words of a similar stem.