Or search: spat, teen, beast, brute, fauna, boyish, junior, orphan, vernal, saxist, actress, girlish, preteen, teenage, untried
2 Syllables: SU
bunches, compass, cumbrous, Dundas, fungus, numbness, oneness, pumice, sumptuous, tonnage, trumpet, unctuous, wondrous
3 Syllables: USU
Columbus, encompass

Found 15 words across 2 groupings. Skipped 3 excess words of a similar stem.