Or search: mortal, someone, somebody, misdating, mistiming
4 Syllables: SUUU
aphorism, Calvinism, cataclysm, catechism, communism, heathenism, humanism, mannerisms, mechanism, naturalism, organism, paganism, unionism
5 Syllables: USUUU
antagonism, determinism, fanaticism, metabolism, sectarianism
7 Syllables: UUUSUUU
utilitarianism

Found 19 words across 3 groupings. Skipped 2 excess words of a similar stem.