Or search: stormy, furious, tearing, vehement, ferocious, merciless, boisterous, unmerciful
2 Syllables: SU
clearer, dearer, hearer, mirror, nearer
3 Syllables: USU
anterior, exterior, inferior, interior, posterior, superior, ulterior

Found 12 words across 2 groupings. Skipped 6 excess words of a similar stem.