Or search: numb, asleep, unaware, benumbed, senseless, anesthetic, unaffected, anaesthetic, insensitive, unconscious, undetectable, imperceptible, unperceivable
3 Syllables: SUU
enviable, genital, plentiful, sensible, sensual, sentinel, temporal, tenable, tentacles, ventricle
4 Syllables: USUU
amenable, commendable, congenital, contemptible, conventional, defensible, dependable, dimensional, intentional, lamentable, ostensible, polemical, presentable, unenviable, unquenchable, untenable
5 Syllables: UUSUU
comprehensible, indefensible, indispensable, reprehensible, unconventional, unintentional

Found 32 words across 3 groupings. Skipped 1 excess word of a similar stem.