3 Syllables: SUU
enviable, plentiful, seminal, sensible, sensual, sentinel, temporal, tentacles, ventricle
4 Syllables: USUU
commendable, contemptible, conventional, defensible, dependable, dimensional, insensible, intentional, lamentable, ostensible, presentable, unenviable, unquenchable
5 Syllables: UUSUU
comprehensible, indefensible, indispensable, reprehensible, unconventional, unintentional

Found 28 words across 3 groupings. Skipped 1 excess word of a similar stem.