Or search: ineffable, untellable, indefinable, unspeakable, unutterable, inexpressible, unexpressible
2 Syllables: SU
spiral
3 Syllables: SUU
friable, liable, Lionel, pliable, sizable, sizeable, viable
4 Syllables: USUU
advisable, assignable, definable, desirable, excitable, inviolable, parietal, reliable
5 Syllables: UUSUU
inadvisable, indefinable, recognizable, undeniable, undesirable, unreliable
6 Syllables: UUUSUU
unjustifiable, unrecognizable

Found 24 words across 5 groupings. Skipped 1 excess word of a similar stem.