Or search: echt, univocal, authentic, veritable, undeniable, unequivocal, indubitable, mathematical, unimpeachable, incontestable, incontestible
3 Syllables: SUU
fashionable, reasonable
4 Syllables: SUUU
estimable, pardonable, questionable, seasonable, treasonable
5 Syllables: USUUU
abominable, companionable, determinable, imaginable, impressionable, inalienable, inestimable, interminable, objectionable, unfashionable, unpardonable, unseasonable
6 Syllables: UUSUUU
unexceptionable

Found 20 words across 4 groupings.