Or search: unbending, inflexible
2 Syllables: SU
actual
3 Syllables: SUU
admirable, capitals, fractional, maximal, taxable, tractable
4 Syllables: USUU
adaptable, compatible, grammatical, implacable, impractical, intractable
5 Syllables: UUSUU
incompatible

Found 14 words across 4 groupings.